Wireless communication methods utilize multiple links, and wireless communication terminals employ this method.

Abstract

The invention relates to a method and apparatus for transmitting traffic, which is performed by a terminal device in a wireless communication system. Specifically, a non-access point STA (access point, AP) under the invention can receive, from the AP, an activation frame that triggers the transmission of a physical layer protocol data unit (PPDU). The activation frame includes information indicating at least one traffic identifier (TID) that is permitted to be transmitted during the target wake time (TWT) period. The TWT period may denote the period in which the transmission of traffic for at least one TID with specific transmission conditions is permitted, and the transmission of traffic without specific transmission conditions is restricted. The non-AP STA then transmits the PPDU, consisting of the traffic corresponding to at least one TID, to the AP during the TWT period.

Description

Wireless communication method using multi-link and wireless communication terminal using the same

[0001] The present invention relates to a wireless communication method using a multi-link and a wireless communication terminal using the same.

[0002]

[0003] With the recent proliferation of mobile devices, wireless LAN (WLAN) technology, which can provide them with fast wireless Internet service, is attracting significant attention. WLAN technology utilizes short-range wireless communication technology to enable mobile devices such as smartphones, tablets, laptops, portable multimedia players, and embedded devices to wirelessly connect to the Internet at home, in businesses, or in specific service areas.

[0004] Since supporting the initial wireless LAN technology using the 2.4 GHz frequency, IEEE (Institute of Electrical and Electronics Engineers) 802.11 has been commercializing or developing various technology standards. First, IEEE 802.11b supports a communication speed of up to 11 Mbps while using the 2.4 GHz band. IEEE 802.11a, which was commercialized after IEEE 802.11b, uses the 5 GHz band instead of the 2.4 GHz band, thereby reducing the impact of interference compared to the considerably crowded 2.4 GHz band. It also uses OFDM (orthogonal frequency division multiplexing) technology to increase the communication speed to up to 54 Mbps. However, IEEE 802.11a has the disadvantage of a shorter communication range than IEEE 802.11b. And IEEE 802.11g, like IEEE 802.11b, uses the 2.4GHz band to achieve a communication speed of up to 54Mbps and satisfies backward compatibility, which has garnered considerable attention. It is also superior to IEEE 802.11a in terms of communication distance.

[0005] And to overcome the limitations of communication speed, which has been pointed out as a vulnerability in wireless LAN, there is IEEE 802.11n, a technical standard established. IEEE 802.11n aims to increase the speed and reliability of networks and extend the operating range of wireless networks. More specifically, IEEE 802.11n supports High Throughput (HT) with data processing speeds of up to 540 Mbps or more, and is based on MIMO (Multiple Inputs and Multiple Outputs) technology that uses multiple antennas at both the transmitter and receiver to minimize transmission errors and optimize data rates. In addition, this standard can use a coding method that transmits multiple redundant copies to increase data reliability.

[0006] As wireless LAN becomes more widespread and applications diversify, the need for new wireless LAN systems that support very high throughput (VHT) higher than the data processing speed supported by IEEE 802.11n has arisen. Among these, IEEE 802.11ac supports a wide bandwidth (80MHz to 160MHz) at the 5GHz frequency. Although the IEEE 802.11ac standard is defined only for the 5GHz band, early 11ac chipsets will also support operation in the 2.4GHz band to ensure backward compatibility with existing 2.4GHz band products. Theoretically, according to this specification, multi-station wireless LAN speeds can reach at least 1Gbps and a maximum single-link speed of at least 500Mbps. This is achieved by extending the wireless interface concepts accepted in 802.11n, such as wider radio frequency bandwidth (up to 160 MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and high-density modulation (up to 256 QAM). In addition, there is IEEE 802.11ad, which transmits data using the 60 GHz band instead of the existing 2.4 GHz / 5 GHz. IEEE 802.11ad is a transmission standard that provides speeds of up to 7 Gbps using beamforming technology, making it suitable for streaming high-bitrate video such as large amounts of data or uncompressed HD video. However, the 60 GHz frequency band has a disadvantage in that it has difficulty passing through obstacles, so it can only be used between devices in short distances.

[0007] Meanwhile, the IEEE 802.11ax (High Efficiency WLAN, HEW) standard, which follows 802.11ac and 802.11ad as a wireless LAN standard, is nearing completion to provide high-efficiency and high-performance wireless LAN communication technology in high-density environments with densely packed APs and terminals. In an 802.11ax-based wireless LAN environment, high-frequency efficient communication must be provided indoors and outdoors in the presence of high-density stations and APs (Access Points), and various technologies have been developed to achieve this.

[0008] Additionally, development of new wireless LAN standards has begun to increase maximum transmission speeds to support emerging multimedia applications such as high-definition video and real-time gaming. The 7th generation wireless LAN standard, IEEE 802.11be (Extremely High Throughput, EHT), is currently under development with the goal of supporting transmission rates of up to 30 Gbps in the 2.4 / 5 / 6 GHz bands through wider bandwidth, increased spatial streams, and multi-AP cooperation.

[0009]

[0010] An embodiment of the present invention aims to provide a wireless communication method using a multi-link and a wireless communication terminal using the same.

[0011] In addition, one embodiment of the present invention aims to provide a method for transmitting traffic in a limited section.

[0012] The technical problems to be achieved in this specification are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0013]

[0014] In a wireless communication system according to the present invention, a terminal (non-AP STA) for transmitting traffic includes a transceiver; and a processor, wherein the processor receives a trigger frame for triggering transmission of a PPDU from an AP (Access Point), wherein the trigger frame includes information indicating at least one TID (Traffic Identifier) ​​whose transmission is permitted in a TWT (Target Wake Time) period, wherein the TWT period indicates a period in which transmission of traffic for the at least one TID having a specific transmission condition is permitted and transmission of traffic not having the specific transmission condition is restricted, and transmits a PPDU (Physical layer Protocol Data Unit) including traffic corresponding to the at least one TID to the AP within the TWT period.

[0015] Additionally, in the present invention, the trigger frame is transmitted within the TWT section.

[0016] Additionally, in the present invention, an MPDU (Medium Access Control: MAC protocol data unit) including traffic corresponding to a TID other than the at least one TID is combined with an MPDU of the PPDU including the traffic corresponding to the at least one TID and transmitted in the form of an A (Aggregated)-MPDU.

[0017] Additionally, in the present invention, traffic for a TID corresponding to the access category of at least one TID is allowed to be transmitted within the TWT section.

[0018] In addition, in the present invention, the TWT section includes a first section and a second section, wherein the first section is a section in which only transmission of the traffic corresponding to the at least one TID is permitted, and the second section is a section in which transmission of traffic corresponding to a TID other than the at least one TID is permitted.

[0019] Additionally, in the present invention, the specific transmission condition is a condition related to transmission delay of traffic.

[0020] Additionally, in the present invention, within the TWT section, a channel access procedure by EDCA (Enhanced Distributed Channel Access) for ACs other than the AC corresponding to the at least one TID is restricted.

[0021] Additionally, in the present invention, the back off counter of the channel access procedure by the EDCA for the other AC within the TWT period is not reduced.

[0022] Additionally, in the present invention, the state of the channel for the channel access procedure by the EDCA for the other AC within the TWT period is a busy state until the TWT period ends.

[0023] In addition, the present invention provides a wireless communication method for receiving a trigger frame that triggers transmission of a PPDU from an AP (Access Point), wherein the trigger frame includes information indicating at least one TID (Traffic Identifier) ​​whose transmission is permitted in a TWT (Target Wake Time) period, wherein the TWT period indicates a period in which transmission of traffic for the at least one TID having a specific transmission condition is permitted and transmission of traffic not having the specific transmission condition is restricted, and transmitting a PPDU (Physical layer Protocol Data Unit) including traffic corresponding to the at least one TID to the AP within the TWT period.

[0024]

[0025] One embodiment of the present invention provides a wireless communication method efficiently using a multi-link and a wireless communication terminal using the same.

[0026] The effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by a person having ordinary skill in the art to which the present invention belongs from the description below.

[0027] Figure 1 illustrates a wireless LAN system according to one embodiment of the present invention.

[0028] Figure 2 illustrates a wireless LAN system according to another embodiment of the present invention.

[0029] Figure 3 shows the configuration of a station according to one embodiment of the present invention.

[0030] Figure 4 shows the configuration of an access point according to one embodiment of the present invention.

[0031] Figure 5 schematically illustrates the process by which a station establishes a link with an access point.

[0032] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0033] Figure 7 illustrates one embodiment of various standard generation-specific PPDU (PLCP Protocol Data Unit) formats.

[0034] FIG. 8 illustrates an example of various Extremely High Throughput (EHT) PPDU formats and a method for indicating the same according to an embodiment of the present invention.

[0035] FIG. 9 is a diagram illustrating a multi-link device according to one embodiment of the present invention.

[0036] FIG. 10 illustrates a method for setting up a broadcast TWT between an AP and a station according to an embodiment of the present invention.

[0037] FIG. 11 shows an AP setting a quiet interval according to an embodiment of the present invention.

[0038] FIG. 12 illustrates a method for setting a TXOP by considering a limited service period of a station according to an embodiment of the present invention.

[0039] FIG. 13 shows a station performing a channel access procedure again considering a limited service period according to an embodiment of the present invention.

[0040] FIG. 14 illustrates an operation of an AP terminating a limited service period early according to an embodiment of the present invention.

[0041] FIG. 15 illustrates an example of a TWT element for setting a broadcast TWT SP (Target Wake Time Service Period) according to an embodiment of the present invention.

[0042] FIG. 16 illustrates an example of a restricted TWT traffic information field for setting a restricted TWT SP according to an embodiment of the present invention.

[0043] FIG. 17 illustrates values ​​of fields included in a Broadcast TWT Parameter Set field according to an embodiment of the present invention.

[0044] FIG. 18 illustrates an example of a format of a trigger frame including information on a TID of traffic that can be transmitted in a limited TWT SP according to an embodiment of the present invention.

[0045] FIG. 19 illustrates an example of the format of a user information field of a trigger frame including information on a TID of traffic that can be transmitted in a limited TWT SP according to an embodiment of the present invention.

[0046] FIG. 20 illustrates an example of an Enhanced Distributed Channel Access (EDCA) operation for channel access in a limited TWT SP according to one embodiment of the present invention.

[0047] FIG. 21 illustrates an example of a method for transmitting traffic for TIDs allowed for transmission and TIDs restricted from transmission in a restricted TWT SP according to one embodiment of the present invention.

[0048] FIG. 22 illustrates an example of how different operating policies are applied to different sections in a single limited TWT SP according to one embodiment of the present invention.

[0049] FIG. 23 is a flowchart illustrating an example of the operation of a terminal according to an embodiment of the present invention.

[0050] The terms used in this specification have been selected from widely used and current terms, taking into account the functions of the present invention. However, these terms may vary depending on the intentions of those skilled in the art, customs, or the emergence of new technologies. Furthermore, in certain cases, the applicant may arbitrarily select terms, in which case their meanings will be described in the description of the relevant invention. Therefore, it should be noted that the terms used in this specification should be interpreted based on their substantive meaning and the overall content of this specification, rather than simply their names.

[0051] Throughout the specification, when a component is said to be "connected" to another component, this includes not only cases where it is "directly connected," but also cases where it is "electrically connected" with another component in between. Furthermore, when a component is said to "include" a specific component, this does not exclude other components, but rather allows the inclusion of other components, unless specifically stated otherwise. Furthermore, the terms "more than" or "less than" based on a specific threshold may be appropriately replaced with "exceeds" or "less than", respectively, depending on the embodiment. In the following, fields and subfields may be used interchangeably in the present invention.

[0052] Figure 1 illustrates a wireless LAN system according to one embodiment of the present invention.

[0053] A wireless LAN system includes one or more Basic Service Sets (BSSs), which represent a collection of devices that have successfully synchronized and can communicate with each other. BSSs can generally be categorized as infrastructure BSSs and independent BSSs (IBSSs). Figure 1 illustrates an infrastructure BSS.

[0054] As illustrated in FIG. 1, the infrastructure BSS (BSS1, BSS2) includes one or more stations (STA1, STA2, STA3, STA4, STA5), an access point (AP-1, AP-2) that provides a distribution service, and a distribution system (DS) that connects multiple access points (AP-1, AP-2).

[0055] A station (STA) is any device that includes a medium access control (MAC) and a physical layer interface for a wireless medium that complies with the IEEE 802.11 standard, and broadly includes both non-access point (AP) stations and access points (APs). In addition, the term "terminal" in this specification may refer to a non-AP STA or an AP, or both. A station for wireless communication includes a processor and a communication unit, and may further include a user interface unit and a display unit, depending on the embodiment. The processor may generate a frame to be transmitted through a wireless network or process a frame received through the wireless network, and may perform various other processes for controlling the station. In addition, the communication unit is functionally connected to the processor and transmits and receives frames through the wireless network for the station. In the present invention, a terminal may be used as a term that includes a user equipment (UE).

[0056] An Access Point (AP) is an entity that provides access to a distribution system (DS) via a wireless medium for stations associated with it. In an infrastructure BSS, communication between non-AP stations is in principle performed via the AP, but direct communication is also possible between non-AP stations when a direct link is established. Meanwhile, in the present invention, the AP is used as a concept including a Personal BSS Coordination Point (PCP), and in a broad sense, it can include concepts such as a centralized controller, a base station (BS), a node-B, a base transceiver system (BTS), or a site controller. In the present invention, the AP may also be referred to as a base wireless communication terminal, and the base wireless communication terminal may be used as a term including, in a broad sense, an AP, a base station, an eNodeB (eNB), and a transmission point (TP). In addition, the base wireless communication terminal may include various types of wireless communication terminals that allocate communication medium resources and perform scheduling in communication with multiple wireless communication terminals.

[0057] Multiple infrastructure BSSs can be interconnected via a distribution system (DS). Multiple BSSs connected via the distribution system are referred to as an Extended Service Set (ESS).

[0058] FIG. 2 illustrates an independent BSS, a wireless LAN system, according to another embodiment of the present invention. Parts of the embodiment of FIG. 2 that are identical or corresponding to those of the embodiment of FIG. 1 will not be redundantly described.

[0059] BSS3, illustrated in Figure 2, is an independent BSS and does not include an AP. Therefore, all stations (STA6, STA7) are not connected to an AP. An independent BSS does not allow access to a distribution system and forms a self-contained network. In an independent BSS, each station (STA6, STA7) can be directly connected to another.

[0060] FIG. 3 is a block diagram showing the configuration of a station (100) according to one embodiment of the present invention. As illustrated, the station (100) according to the embodiment of the present invention may include a processor (110), a communication unit (120), a user interface unit (140), a display unit (150), and a memory (160).

[0061] First, the communication unit (120) transmits and receives wireless signals such as wireless LAN packets, and may be built into or externally installed in the station (100). According to an embodiment, the communication unit (120) may include at least one communication module using different frequency bands. For example, the communication unit (120) may include communication modules of different frequency bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. According to one embodiment, the station (100) may include a communication module using a frequency band of 7.125 GHz or higher and a communication module using a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with an AP or an external station according to the wireless LAN standard of the frequency band supported by the corresponding communication module. The communication unit (120) may operate only one communication module at a time or may operate multiple communication modules simultaneously, depending on the performance and requirements of the station (100). When the station (100) includes multiple communication modules, each communication module may be provided in an independent form, or the multiple modules may be integrated into a single chip. In the embodiment of the present invention, the communication unit (120) may represent an RF (Radio Frequency) communication module that processes RF (Radio Frequency) signals.

[0062] Next, the user interface unit (140) includes various types of input / output means provided in the station (100). That is, the user interface unit (140) can receive user input using various input means, and the processor (110) can control the station (100) based on the received user input. In addition, the user interface unit (140) can perform output based on a command of the processor (110) using various output means.

[0063] Next, the display unit (150) outputs an image on the display screen. The display unit (150) can output various display objects, such as content executed by the processor (110) or a user interface based on the control commands of the processor (110). In addition, the memory (160) stores a control program used in the station (100) and various data corresponding thereto. Such a control program may include a connection program required for the station (100) to connect to an AP or an external station.

[0064] The processor (110) of the present invention can execute various commands or programs and process data within the station (100). In addition, the processor (110) can control each unit of the above-described station (100) and control data transmission and reception between the units. According to an embodiment of the present invention, the processor (110) can execute a program for connection to an AP stored in the memory (160) and receive a communication setup message transmitted by the AP. In addition, the processor (110) can read information on the priority conditions of the station (100) included in the communication setup message and request connection to the AP based on the information on the priority conditions of the station (100). The processor (110) of the present invention may refer to the main control unit of the station (100), and according to an embodiment, may refer to a control unit for individually controlling some components of the station (100), such as the communication unit (120). That is, the processor (110) may be a modem or modulator and / or demodulator that modulates and / or demodulates wireless signals transmitted and received from the communication unit (120). The processor (110) controls various operations of transmitting and receiving wireless signals of the station (100) according to an embodiment of the present invention. A specific embodiment thereof will be described later.

[0065] The station (100) illustrated in FIG. 3 is a block diagram according to one embodiment of the present invention, and the blocks shown separately are logically distinguished elements of the device. Accordingly, the elements of the above-described device may be mounted as one chip or as multiple chips depending on the design of the device. For example, the processor (110) and the communication unit (120) may be implemented by being integrated into one chip or may be implemented as separate chips. In addition, in the embodiment of the present invention, some components of the station (100), such as the user interface unit (140) and the display unit (150), may be selectively provided in the station (100).

[0066] Fig. 4 is a block diagram illustrating the configuration of an AP (200) according to one embodiment of the present invention. As illustrated, the AP (200) according to the embodiment of the present invention may include a processor (210), a communication unit (220), and a memory (260). In Fig. 4, redundant descriptions of portions of the configuration of the AP (200) that are identical or corresponding to the configuration of the station (100) of Fig. 3 will be omitted.

[0067] Referring to FIG. 4, the AP (200) according to the present invention has a communication unit (220) for operating a BSS in at least one frequency band. As described above in the embodiment of FIG. 3, the communication unit (220) of the AP (200) may also include a plurality of communication modules that utilize different frequency bands. That is, the AP (200) according to the embodiment of the present invention may include two or more communication modules for different frequency bands, such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz. Preferably, the AP (200) may include a communication module that utilizes a frequency band of 7.125 GHz or higher and a communication module that utilizes a frequency band of 7.125 GHz or lower. Each communication module may perform wireless communication with a station according to the wireless LAN standard of the frequency band supported by the corresponding communication module. The communication unit (220) may operate only one communication module at a time or may operate multiple communication modules simultaneously, depending on the performance and requirements of the AP (200). In an embodiment of the present invention, the communication unit (220) may represent an RF communication module that processes an RF (Radio Frequency) signal.

[0068] Next, the memory (260) stores the control program used in the AP (200) and various data according to the control program. This control program may include a connection program that manages the connection of the station. In addition, the processor (210) controls each unit of the AP (200) and may control data transmission and reception between the units. According to an embodiment of the present invention, the processor (210) may execute a program for connection with a station stored in the memory (260) and transmit a communication setup message to one or more stations. At this time, the communication setup message may include information on the connection priority conditions of each station. In addition, the processor (210) performs connection setup according to a connection request from a station. According to one embodiment, the processor (210) may be a modem or a modulator and / or demodulator that modulates and demodulates a wireless signal transmitted and received from the communication unit (220). The processor (210) controls various operations of wireless signal transmission and reception of the AP (200) according to an embodiment of the present invention. Specific examples of this will be described later.

[0069] Figure 5 schematically illustrates the process by which a station establishes a link with an access point.

[0070] Referring to FIG. 5, the link between STA (100) and AP (200) is largely established through three stages: scanning, authentication, and association. First, the scanning stage is a stage in which STA (100) acquires access information of a BSS operated by AP (200). Methods for performing scanning include a passive scanning method in which information is acquired only by utilizing a beacon message (S101) periodically transmitted by AP (200), and an active scanning method in which STA (100) acquires access information by transmitting a probe request to AP (S103) and receiving a probe response from AP (S105).

[0071] The STA (100) that successfully receives wireless access information in the scanning step transmits an authentication request (S107a) and receives an authentication response from the AP (200) (S107b) to perform the authentication step. After the authentication step is performed, the STA (100) transmits an association request (S109a) and receives an association response from the AP (200) (S109b) to perform the association step. In this specification, association basically means wireless association, but the present invention is not limited thereto, and association in a broad sense may include both wireless association and wired association.

[0072] Meanwhile, an additional 802.1X-based authentication step (S111) and an IP address acquisition step (S113) via DHCP may be performed. In Fig. 5, the authentication server (300) is a server that processes STA (100) and 802.1X-based authentication, and may be physically connected to the AP (200) or may exist as a separate server.

[0073] Figure 6 shows an example of a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method used in wireless LAN communication.

[0074] A terminal performing wireless LAN communication performs carrier sensing before transmitting data to check whether the channel is busy. If a wireless signal above a certain strength is detected, the channel is determined to be busy, and the terminal delays access to the channel. This process is called clear channel assessment (CCA), and the level that determines whether the signal is detected is called the CCA threshold. If a wireless signal above the CCA threshold received by the terminal is intended for the terminal, the terminal processes the received wireless signal. On the other hand, if no wireless signal is detected on the channel or a wireless signal with a strength lower than the CCA threshold is detected, the channel is determined to be idle.

[0075] When the channel is determined to be idle, each terminal with data to transmit performs a backoff procedure after an Inter Frame Space (IFS) time, such as an Arbitration IFS (AIFS) or a PCF IFS (PIFS), depending on the status of each terminal. In some embodiments, the AIFS may be used as a configuration to replace the existing DIFS (DCF IFS). Each terminal waits while decreasing the slot time by a random number determined for the terminal during the interval of the channel's idle state, and a terminal that has exhausted all of its slot time attempts to access the channel. The period during which each terminal performs the backoff procedure is called a contention window period.

[0076] If a specific terminal successfully accesses the channel, the terminal can transmit data through the channel. However, if the terminal attempting access collides with another terminal, the collided terminals are each assigned a new random number and perform a backoff procedure again. According to one embodiment, the random number newly assigned to each terminal may be determined within a range twice (2*CW) of the random number range (contention window, CW) previously assigned to the terminal. Meanwhile, each terminal performs the backoff procedure again in the next contention window period to attempt access, and at this time, each terminal performs the backoff procedure starting from the slot time remaining in the previous contention window period. In this way, each terminal performing wireless LAN communication can avoid collisions with each other for a specific channel.

[0077] Hereinafter, in the present invention, a terminal may be referred to as a non-AP STA, an AP STA, an AP, an STA, a receiving device, or a transmitting device, and the present invention is not limited thereto. In addition, in the present invention, an AP STA may be referred to as an AP.

[0078] <Various PPDU format examples>

[0079] Fig. 7 illustrates examples of various standard generation-specific PPDU (PLCP Protocol Data Unit) formats. More specifically, Fig. 7(a) illustrates an embodiment of a legacy PPDU format based on 802.11a / g, Fig. 7(b) illustrates an embodiment of a HE PPDU format based on 802.11ax, and Fig. 7(c) illustrates an embodiment of a non-legacy PPDU (i.e., EHT PPDU) format based on 802.11be. In addition, Fig. 7(d) illustrates detailed field configurations of L-SIG and RL-SIG commonly used in the above PPDU formats.

[0080] Referring to FIG. 7(a), the preamble of a legacy PPDU includes a legacy short training field (L-STF), a legacy long training field (L-LTF), and a legacy signal field (L-SIG). In an embodiment of the present invention, the L-STF, L-LTF, and L-SIG may be referred to as a legacy preamble.

[0081] Referring to FIG. 7(b), the preamble of the HE PPDU additionally includes RL-SIG (Repeated Legacy Short Training field), HE-SIG-A (High Efficiency Signal A field), HE-SIG-B (High Efficiency Signal B field), HE-STF (High Efficiency Short Training field), and HE-LTF (High Efficiency Long Training field) in addition to the legacy preamble. In an embodiment of the present invention, the RL-SIG, HE-SIG-A, HE-SIG-B, HE-STF, and HE-LTF may be referred to as a HE preamble. The specific configuration of the HE preamble may be modified according to the HE PPDU format. For example, HE-SIG-B may be used only in the HE MU PPDU format.

[0082] Referring to FIG. 7(c), the preamble of the EHT PPDU additionally includes, in addition to the legacy preamble, an RL-SIG (Repeated Legacy Short Training field), a U-SIG (Universal Signal field), an EHT-SIG-A (Extremely High Throughput Signal A field), an EHT-SIG-A (Extremely High Throughput Signal B field), an EHT-STF (Extremely High Throughput Short Training field), and an EHT-LTF (Extremely High Throughput Long Training field). In an embodiment of the present invention, the RL-SIG, EHT-SIG-A, EHT-SIG-B, EHT-STF, and EHT-LTF may be referred to as an EHT preamble. The specific configuration of the non-legacy preamble may be modified according to the EHT PPDU format. For example, EHT-SIG-A and EHT-SIG-B may be used only in some of the EHT PPDU formats.

[0083] The L-SIG field included in the PPDU preamble applies 64FFT OFDM and consists of a total of 64 subcarriers. Of these, 48 subcarriers, excluding the guard subcarrier, DC subcarrier, and pilot subcarrier, are used for L-SIG data transmission. Since L-SIG applies BPSK, Rate=1 / 2 Modulation and Coding Scheme (MCS), it can contain a total of 24 bits of information. Figure 7(d) shows the 24-bit information structure of L-SIG.

[0084] Referring to Fig. 7(d), L-SIG includes an L_RATE field and an L_LENGTH field. The L_RATE field consists of 4 bits and indicates the MCS used for data transmission. Specifically, the L_RATE field indicates one of the transmission speeds of 6 / 9 / 12 / 18 / 24 / 36 / 48 / 54 Mbps, which combine modulation methods such as BPSK / QPSK / 16-QAM / 64-QAM and inefficiencies such as 1 / 2, 2 / 3, and 3 / 4. Combining the information in the L_RATE field and the L_LENGTH field can indicate the total length of the corresponding PPDU. In non-legacy PPDU formats, the L_RATE field is set to the minimum speed of 6 Mbps.

[0085] The L_LENGTH field is allocated in bytes, with a total of 12 bits, allowing for signaling up to 4095. In combination with the L_RATE field, it can indicate the length of the corresponding PPDU. At this time, legacy and non-legacy terminals may interpret the L_LENGTH field in different ways.

[0086] First, the method by which a legacy terminal or non-legacy terminal interprets the length of the PPDU using the L_LENGTH field is as follows. If the value of the L_RATE field is set to indicate 6 Mbps, 3 bytes (i.e., 24 bits) can be transmitted during 4 us, which is the duration of one symbol of 64 FFT. Therefore, by adding 3 bytes corresponding to the SVC field and Tail field to the L_LENGTH field value and dividing this by 3 bytes, which is the transmission amount of one symbol, the number of symbols based on 64 FFT after L-SIG is obtained. Multiplying the obtained number of symbols by 4 us, which is the duration of one symbol, and then adding 20 us required for transmission of L-STF, L-LTF, and L-SIG, the length of the PPDU, i.e., the reception time (RXTIME) is obtained. This can be expressed as a formula as shown in Mathematical Expression 1 below.

[0087]

[0088] At this time, represents the smallest natural number greater than or equal to x. Since the maximum value of the L_LENGTH field is 4095, the length of the PPDU can be set to a maximum of 5.484 ms. A non-legacy terminal transmitting the PPDU must set the L_LENGTH field as in Mathematical Expression 2 below.

[0089]

[0090] Here, TXTIME is the total transmission time that constitutes the corresponding PPDU, as shown in mathematical expression 3 below. In this case, TX represents the transmission time of X.

[0091]

[0092] Referring to the above formulas, the length of the PPDU is calculated based on the rounded value of L_LENGTH / 3. Therefore, for any value of k, three different values ​​of L_LENGTH={3k+1, 3k+2, 3(k+1)} indicate the same PPDU length.

[0093] Referring to Fig. 7(e), the U-SIG (Universal SIG) field continues to exist in EHT PPDUs and subsequent generation wireless LAN PPDUs, and serves to distinguish which generation of PPDU it is, including 11be. U-SIG is an OFDM 2 symbol based on 64FFT and can convey a total of 52 bits of information. Of these, 43 bits, excluding the 9 bits of CRC / Tail, are largely divided into the VI (Version Independent) field and the VD (Version Dependent) field.

[0094] The VI bit maintains its current bit configuration in the future so that even if a subsequent generation PPDU is defined, current 11be terminals can obtain information about the PPDU through the VI fields of the PPDU. To this end, the VI field consists of PHY version, UL / DL, BSS Color, TXOP, and Reserved fields. The PHY version field is 3 bits and sequentially distinguishes 11be and subsequent generation wireless LAN standards by version. For 11be, it has a value of 000b. The UL / DL field distinguishes whether the PPDU is an uplink / downlink PPDU. BSS Color means an identifier for each BSS defined in 11ax and has a value of 6 bits or more. TXOP means the Transmit Opportunity Duration that was carried in the MAC header. By adding it to the PHY header, the length of the TXOP including the PPDU can be inferred without having to decode the MPDU (Medium Access Control: MAC protocol data unit), and has a value of 7 bits or more.

[0095] The VD field is signaling information that is only useful for PPDUs of version 11be. It can be composed of fields that are commonly used in any PPDU format, such as PPDU format and BW, and fields that are defined differently for each PPDU format. The PPDU format is a delimiter that distinguishes EHT SU (Single User), EHT MU (Multiple User), EHT TB (Trigger-based), and EHT ER (Extended Range) PPDUs. The BW field signals five basic PPDU BW options (a BW that can be expressed in the form of an exponential power of 20*2 can be called a basic BW) of 20, 40, 80, 160 (80+80), and 320 (160+160) MHz, as well as various remaining PPDU BWs configured through Preamble Puncturing. In addition, after being signaled at 320 MHz, some 80 MHz can be signaled in a punctured form. Additionally, the punctured and modified channel shape can be signaled directly in the BW field, or can be signaled using the BW field together with a field appearing after the BW field (e.g., a field within the EHT-SIG field). If the BW field is 3 bits, a total of 8 BW signaling is possible, so only 3 puncturing modes can be signaled at most. If the BW field is 4 bits, a total of 16 BW signaling is possible, so a maximum of 11 puncturing modes can be signaled.

[0096] The fields located after the BW field vary depending on the type and format of the PPDU. MU PPDUs and SU PPDUs can be signaled in the same PPDU format, and a field to distinguish between MU PPDUs and SU PPDUs can be located before the EHT-SIG field, and additional signaling can be performed for this. Both SU PPDUs and MU PPDUs include the EHT-SIG field, but some fields that are not necessary in the SU PPDU may be compressed. In this case, the information in the compressed fields may be omitted or may have a reduced size compared to the original fields included in the MU PPDU. For example, in the case of the SU PPDU, the common field of the EHT-SIG may be omitted or replaced, or the user-specific field may be replaced or reduced to one, etc., and may have a different configuration.

[0097] Alternatively, the SU PPDU may further include a compression field indicating whether compression is performed, and some fields (e.g., RA field, etc.) may be omitted depending on the value of the compression field.

[0098] If part of the EHT-SIG field of the SU PPDU is compressed, information to be included in the compressed field may be signaled together in an uncompressed field (e.g., a common field, etc.). In the case of the MU PPDU, since it is a PPDU format for simultaneous reception by multiple users, the EHT-SIG field must be transmitted after the U-SIG field, and the amount of signaled information may be variable. That is, since multiple MU PPDUs are transmitted to multiple STAs, each STA must recognize the location of the RU to which the MU PPDU is transmitted, the STA to which each RU is allocated, and whether the transmitted MU PPDU was transmitted to itself. Therefore, the AP must include and transmit the above information in the EHT-SIG field. To this end, the U-SIG field signals information for efficiently transmitting the EHT-SIG field, which may be the number of symbols in the EHT-SIG field and / or the MCS modulation method. The EHT-SIG field may include information on the size and location of the RU allocated to each user.

[0099] In the case of an SU PPDU, multiple RUs may be allocated to an STA, and the multiple RUs may or may not be consecutive. If the RUs allocated to the STA are not consecutive, the STA must recognize RUs that are punctured in the middle to efficiently receive the SU PPDU. Therefore, the AP may transmit information on punctured RUs among the RUs allocated to the STA in the SU PPDU (e.g., puncturing patterns of the RUs). That is, in the case of an SU PPDU, a puncturing mode field including information indicating whether a puncturing mode is applied and a puncturing pattern in a bitmap format, etc., may be included in the EHT-SIG field, and the puncturing mode field may signal the type of a discontinuous channel that appears within the bandwidth.

[0100] The form of the signaled discontinuous channel is limited, and the BW and discontinuous channel information of the SU PPDU are indicated in combination with the value of the BW field. For example, in the case of the SU PPDU, since it is a PPDU transmitted to only a single terminal, the STA can recognize the bandwidth allocated to it through the BW field included in the PPDU, and can recognize the punctured resource among the allocated bandwidth through the puncturing mode field of the U-SIG field or EHT-SIG field included in the PPDU. In this case, the terminal can receive the PPDU in the remaining resource units except for a specific channel of the punctured resource unit. At this time, multiple RUs allocated to the STA may be configured with different frequency bands or tones.

[0101] The reason why only a limited number of discontinuous channel types are signaled is to reduce the signaling overhead of the SU PPDU. Since puncturing can be performed on a per-20 MHz subchannel basis, if puncturing is performed on a BW with multiple 20 MHz subchannels, such as 80, 160, and 320 MHz, the discontinuous channel type (if only the edge 20 MHz is punctured, it is also considered discontinuous) must be signaled by individually indicating whether the remaining 15 20 MHz subchannels, excluding the primary channel, are used. Dedicating 15 bits to signaling the discontinuous channel type of single-user transmission can result in excessive signaling overhead considering the low data rate of the signaling portion.

[0102] The present invention proposes a technique for signaling the discontinuous channel type of an SU PPDU, and illustrates the discontinuous channel type determined according to the proposed technique. In addition, the present invention proposes a technique for signaling the puncturing types of the Primary 160 MHz and Secondary 160 MHz in a 320 MHz BW configuration of an SU PPDU, respectively.

[0103] In addition, one embodiment of the present invention proposes a technique for differentiating the configuration of a PPDU indicated by preamble puncturing BW values ​​according to the PPDU format signaled in the PPDU format field. Assuming that the BW field is 4 bits long, in the case of an EHT SU PPDU or a TB PPDU, an EHT-SIG-A of 1 symbol may be additionally signaled after the U-SIG, or EHT-SIG-A may not be signaled at all. Therefore, considering this, it is necessary to fully signal up to 11 puncturing modes through only the BW field of the U-SIG. However, in the case of an EHT MU PPDU, an EHT-SIG-B is additionally signaled after the U-SIG, so up to 11 puncturing modes can be signaled in a different way from the SU PPDU. In the case of an EHT ER PPDU, the BW field can be set to 1 bit to signal whether the PPDU uses a 20 MHz or 10 MHz band.

[0104] Figure 7(f) illustrates the configuration of the Format-specific field of the VD field when the PPDU format field of the U-SIG indicates an EHT MU PPDU. In the case of the MU PPDU, the SIG-B signaling field for simultaneous reception by multiple users is essential, and SIG-B can be transmitted after the U-SIG without a separate SIG-A. To this end, the U-SIG must signal information for decoding SIG-B. These fields include the SIG-B MCS, SIG-B DCM, Number of SIG-B Symbols, SIG-B Compression, and Number of EHT-LTF Symbols fields.

[0105] FIG. 8 illustrates an example of various Extremely High Throughput (EHT) PPDU formats and a method for indicating the same according to an embodiment of the present invention.

[0106] Referring to FIG. 8, a PPDU can be composed of a preamble and a data portion, and the format of one type of EHT PPDU can be distinguished according to the U-SIG field included in the preamble. Specifically, whether the format of the PPDU is an EHT PPDU can be indicated based on the PPDU format field included in the U-SIG field.

[0107] Figure 8 (a) shows an example of an EHT SU PPDU format for a single STA. The EHT SU PPDU is a PPDU used for single user (SU) transmission between an AP and a single STA, and an EHT-SIG-A field for additional signaling may be located after the U-SIG field.

[0108] Figure 8 (b) shows an example of the EHT Trigger-based PPDU format, which is an EHT PPDU transmitted based on a trigger frame. The EHT Trigger-based PPDU is an EHT PPDU transmitted based on a trigger frame and is an uplink PPDU used for responding to the trigger frame. Unlike the EHT SU PPDU, the EHT PPDU does not have an EHT-SIG-A field located after the U-SIG field.

[0109] Figure 8 (c) illustrates an example of the EHT MU PPDU format, which is an EHT PPDU for multiple users. The EHT MU PPDU is a PPDU used to transmit a PPDU to one or more STAs. The EHT MU PPDU format may include a HE-SIG-B field after the U-SIG field.

[0110] Fig. 8(d) illustrates an example of an EHT ER SU PPDU format used for single-user transmission with STAs in an extended range. The EHT ER SU PPDU can be used for single-user transmission with STAs in a wider range than the EHT SU PPDU described in Fig. 8(a), and the U-SIG field can be repeatedly positioned on the time axis.

[0111] The EHT MU PPDU described in (c) of FIG. 8 can be used by an AP for downlink transmission to multiple STAs. At this time, the EHT MU PPDU can include scheduling information so that multiple STAs can simultaneously receive the PPDU transmitted from the AP. The EHT MU PPDU can transmit AID information of the receiver and / or transmitter of the PPDU transmitted through the user specific field of EHT-SIG-B to the STA. Accordingly, multiple terminals receiving the EHT MU PPDU can perform a spatial reuse operation based on the AID information of the user specific field included in the preamble of the received PPDU.

[0112] Specifically, the resource unit allocation (RA) field of the HE-SIG-B field included in the HE MU PPDU may include information about the configuration of resource units (e.g., the partitioning form of resource units) in a specific bandwidth (e.g., 20 MHz, etc.) of the frequency axis. That is, the RA field may indicate the configuration of resource units partitioned in the bandwidth for transmission of the HE MU PPDU for the STA to receive the PPDU. Information about the STA allocated (or designated) to each partitioned resource unit may be included in the user-specific field of the EHT-SIG-B and transmitted to the STA. That is, the user-specific field may include one or more user fields corresponding to each partitioned resource unit.

[0113] For example, among the multiple resource units that are divided, a user field corresponding to at least one resource unit used for data transmission may include an AID of a receiver or a sender, and a user field corresponding to the remaining resource unit(s) that are not used for data transmission may include a preset null STA ID.

[0114] Two or more PPDUs illustrated in FIG. 8 can be indicated with a value indicating the same PPDU format. That is, two or more PPDUs can be indicated with the same PPDU format through the same value. For example, EHT SU PPDU and EHT MU PPDU can be indicated with the same value through the U-SIG PPDU format subfield. At this time, EHT SU PPDU and EHT MU PPDU can be distinguished by the number of STAs receiving the PPDU. For example, a PPDU received by only one STA can be identified as an EHT SU PPDU, and if the number of STAs is set so that two or more STAs receive it, it can be identified as an EHT MU PPDU. In other words, two or more PPDU formats illustrated in FIG. 8 can be indicated through the same subfield value.

[0115] In addition, among the fields illustrated in FIG. 8, some fields or some information of the fields may be omitted, and a case in which some fields or some information of the fields are omitted may be defined as compression mode or compressed mode.

[0116] FIG. 9 is a diagram illustrating a multi-link device according to one embodiment of the present invention.

[0117] Referring to FIG. 9, the concept of a device that is affiliated with one or more STAs may be defined. In another embodiment, according to one embodiment of the present invention, devices that are affiliated with more than one STA (i.e., two or more) may be defined. In this case, the device may be a logical concept. Accordingly, devices that are affiliated with one or more or more than one STA of this concept may be referred to as a multi-link device (MLD), a multi-band device, or a multi-link logical entity (MLLE).

[0118] Alternatively, the devices of the above concept may be referred to as multi-link entities (MLEs). Furthermore, an MLD may have one medium access control service access point (MAC SAP) up to a logical link control (LLC), and an MLD may have one MAC data service.

[0119] STAs included in MLD can operate on more than one link or channel. That is, STAs included in MLD can operate on multiple different channels. For example, STAs included in MLD can operate using channels in different frequency bands of 2.4 GHz, 5 GHz, and 6 GHz. Through this, MLD can gain advantages in channel access and improve the performance of the overall network. While conventional wireless LANs operate on a single link, MLD operation can obtain more channel access opportunities by utilizing multiple links, or STAs can operate efficiently on multiple links by considering channel conditions.

[0120] Additionally, if the STAs affiliated with an MLD are APs, the MLD to which the APs are affiliated may be an AP MLD. However, if the STAs affiliated with an MLD are non-AP STAs, the MLD to which the non-APs are affiliated may be a non-AP MLD.

[0121] Additionally, an AP MLD (Multi-link Device) may be a device that includes one or more wireless access points (APs), and may be a device connected to a higher layer through a single interface. That is, an AP MLD may be connected to the Logical Link Control (LLC) layer through a single interface. Multiple APs included in an AP MLD may share some functions in the MAC layer. Each AP within an AP MLD may operate on a different link. An STA MLD may be a device that includes one or more non-AP STAs, and may be a device connected to a higher layer through a single interface.

[0122] That is, the STA MLD can be connected to the LLC layer through a single interface. Multiple STAs included in the STA MLD can share some functions in the MAC layer. In addition, the STA MLD can be called a non-AP MLD. At this time, the AP MLD and the STA MLD can perform a multi-link operation that communicates using multiple individual links. That is, when the AP MLD includes multiple APs, each AP can configure a separate link and perform frame transmission and reception operations using multiple links with each terminal included in the STA MLD. At this time, each link can operate in the 2.4 GHz, 5 GHz, or 6 GHz band, and each link can perform a bandwidth expansion operation. For example, if the AP MLD sets up one link in the 2.4 GHz band and two links in the 5 GHz band, frame transmission can be performed with a bandwidth of 40 MHz through bandwidth expansion in the 2.4 GHz band, and frame transmission can be performed with a bandwidth of up to 320 MHz by utilizing non-contiguous bandwidth in each link using the 5 GHz band.

[0123] Meanwhile, in the AP MLD or STA MLD, while one terminal in the MLD is performing a transmission operation, another terminal may not be able to perform a reception operation due to an interference problem within the device. In this way, the operation in which another AP or terminal in the MLD receives while one AP or terminal is performing a transmission operation within the MLD is called STR (Simultaneous Transmit and Receive). The AP MLD may enable STR operation for all links. Alternatively, the STR operation may not be possible for some links of the AP MLD. A terminal MLD capable of STR operation may be connected to the AP MLD, and an MLD incapable of STR operation may be connected for some or all links. In addition, a terminal (e.g., IEEE 802.11a / b / g / n / ac / ax terminal) that does not belong to the MLD may be additionally connected to an AP included in the AP MLD.

[0124] The AP MLD and the STA MLD can perform a negotiation process for multi-link usage operation during the scanning and connection process described in FIG. 5. For example, during the scanning process described in FIG. 5, an AP included in the AP MLD can transmit a beacon frame including an indicator indicating that multi-link operation is available, the number of available links, and information on multiple available links. Alternatively, a terminal belonging to the STA MLD can transmit a probe request frame including an indicator indicating that multi-link operation is available, and an AP belonging to the AP MLD can include an indicator indicating that multi-link operation is available in a probe response frame. In this case, the AP can additionally transmit information such as the number of available links and link information during multi-link operation.

[0125] In the above scanning process, the STA MLD, which has confirmed whether the AP MLD performs multi-link operation and the link information used, can perform a connection process with the AP MLD. At this time, the AP MLD and the STA MLD can start a negotiation process for multi-link operation. At this time, the negotiation process for multi-link operation can be performed during a connection process between an AP belonging to the AP MLD and a terminal belonging to the STA MLD. That is, any terminal belonging to the STA MLD (e.g., STA1) can send a connection request frame to any AP belonging to the AP MLD (e.g., AP1) while sending an indicator indicating that the terminal's multi-link operation is available and a request indicator requesting to perform the multi-link operation. The AP, which has received the connection request frame from the terminal, can confirm the indicator requesting the multi-link operation, and if the AP is capable of multi-link operation, can transmit an connection response frame to the terminal, which allows the multi-link operation, including link information to be used for the multi-link operation and parameters used in each link. The parameters for the above multi-link operation may include one or more of the bandwidth of each link used, the direction of bandwidth expansion, the Target Beacon Transmission Time (TBTT), and whether STR is in operation. The AP MLD and STA MLD, in which the use of multi-link operation is confirmed by exchanging the connection request frame and response frame, may perform frame transmission operation using multiple links using multiple APs included in the AP MLD and multiple terminals included in the STA MLD after the connection process.

[0126] Referring to FIG. 9, there may be an MLD including multiple STAs, and multiple STAs included in the MLD may operate on multiple links. In FIG. 9, an MLD including APs AP1, AP2, and AP3 may be referred to as an AP MLD, and an MLD including non-AP STAs non-AP STA1, non-AP STA2, and non-AP STA3 may be referred to as a non-AP MLD. The STAs included in the MLD may operate on Link 1, Link 2, Link 3, or some of Links 1 to 3.

[0127] According to an embodiment of the present invention, a multi-link operation may include a multi-link setup operation. The multi-link setup operation may be an operation corresponding to an association performed in a single-link operation. In order to exchange frames in multiple links, multi-link setup may have to be performed first. The multi-link setup operation may be performed using a multi-link setup element. Here, the multi-link setup element may include capability information related to the multi-link, and the capability information may include information related to a link through which an STA included in the MLD can receive a frame while another STA included in the MLD can transmit a frame through another link. That is, the capability information may include information related to whether STAs (non-AP STAs and / or APs (or AP STAs) can simultaneously transmit / receive frames in different transmission directions through the links included in the MLD. In addition, the capability information may further include information related to available links or operating channels. Multi-link setup may be established through negotiation between peer STAs, and multi-link operation may be established through one link.

[0128] According to one embodiment of the present invention, a mapping relationship may exist between a TID and a link of an MLD. For example, when a TID and a link are mapped, the TID may be transmitted through the mapped link. The mapping between the TID and the link may be directional-based. For example, mapping may be performed for each of the two directions between MLD1 and MLD2. Furthermore, the mapping between the TID and the link may have a default setting. For example, the mapping between the TID and the link may be such that all TIDs are mapped to a certain link by default.

[0129] FIG. 10 illustrates a method for setting up a broadcast TWT between an AP and a station according to an embodiment of the present invention.

[0130] In TWT, the service period can be set as follows. The AP requests the station associated with the AP to participate in TWT. The station can participate in broadcast TWT or negotiate an individual TWT with the AP. At this time, the AP can request the station to participate in TWT by setting the value of the TWT Required subfield of the HE Operation element to 1. In addition, the AP can transmit the Broadcast TWT element through a management frame, such as a beacon frame, to provide the station with information necessary for participation in broadcast TWT. At this time, the AP can signal that it supports broadcast TWT by setting dot11TWTOptionActivated to true and setting the Broadcast TWT Support field (of the element) of the HE Capabilities element to 1. The AP can set a limited service period similar to the service period of TWT.

[0131] In the embodiment of FIG. 10, the first station (STA1) requests the AP to set up TWT. The AP and the first station (STA1) set up TWT parameters, such as an initial TBTT and a listen interval. Accordingly, the AP and the first station (STA1) and the second station (STA2) set up a broadcast TWT. The AP indicates a broadcast TWT service period using a beacon frame. In the broadcast TWT service period, the AP can transmit a downlink (DL) physical layer protocol data unit (PPDU) to the first station (STA1) and the second station (STA2) or transmit a trigger frame to the first station (STA1) and the second station (STA2) to trigger an uplink (UL) transmission. In the broadcast TWT service period, the first station (STA1) and the second station (STA2) wake up to receive the beacon frame. The first station (STA1) and the second station (STA2) obtain information about TWT from the received beacon frame. The AP transmits a trigger frame to the first station (STA1) and the second station (STA2), the first station (STA1) transmits a PS-Poll frame to the AP, and the second station (STA2) transmits a QoS Null frame to the AP. The AP receives the PS-Poll frame and the QoS Null frame transmitted by the first station (STA1) and the second station (STA2), and determines that the first station (STA1) and the second station (STA2) are in an awake state. The AP transmits a multi-STA Block ACK frame to the first station (STA1) and the second station (STA2). The AP transmits a DL PPDU to the first station (STA1) and the second station (STA2).

[0132] Existing TWT service periods do not restrict non-TWT stations from accessing channels or transmitting. This is because TWT is intended to facilitate stations participating in TWT entering a doze state. However, limited service periods, intended to prevent transmission delays for low-latency traffic, must ensure priority transmission of low-latency traffic. Therefore, a method to protect limited service periods is needed.

[0133] During a limited service period, stations that do not participate in the limited TWT may be restricted from accessing the channel. Specifically, during a limited service period, stations that do not participate in the limited TWT may not be able to perform channel access. During a limited service period, if a station that does not participate in the limited TWT completes channel access, the station may restart the channel access procedure without performing transmission. At this time, the station may restart the channel access procedure when the limited service period ends. In other words, restarting channel access during a limited service period may mean suspending transmission, such as re-selecting the back-off counter to restart channel access. When the limited service period ends, it may mean attempting channel access again because channel access is allowed again.

[0134] Additionally, a station's channel access may indicate an EDCA backoff procedure. Completing a channel access may indicate that the backoff counter of the EDCA backoff procedure has reached 0. Additionally, when a station restarts the channel access procedure, the station may randomly obtain an integer within the CW used for the previous channel access and use the obtained integer as the backoff counter. That is, the station may not double the size of the CW used for the previous channel access. In this case, the CW may be maintained per AC. This channel access restriction may only be applied to stations that support restricted TWT. Specifically, this channel access restriction may only be applied to non-legacy (EHT) stations for which the dot11RestrictedTWTOptionImplemented property of the EHT Capabilities element is set to true, and may not be applied to non-legacy (EHT) stations for which the dot11RestrictedTWTOptionImplemented property of the EHT Capabilities element is set to false. In this specification, a non-legacy station may refer to an EHT station and a post-EHT station. Furthermore, a legacy station may refer to a pre-EHT station, such as a non-HT station, an HT station, a VHT station, or an HE station.

[0135] Additionally, during a limited service period, a NAV may be set for non-legacy stations for traffic other than low-latency traffic. Specifically, as if a NAV had been set for traffic other than low-latency traffic, the station may suspend channel access procedures for transmission of traffic other than low-latency traffic. In this embodiment, the NAV may be a NAV independent from a conventional NAV (basic NAV, intra-BSS NAV). In this case, non-legacy stations may be limited to stations that support limited TWT. In another specific embodiment, non-legacy stations may be limited to stations that participate in limited TWT.

[0136] The limited service period may be included within a broadcast TWT service period. In another specific embodiment, the limited service period may not be included within a broadcast TWT service period.

[0137] Additionally, the limited service period can be repeated periodically as specified by the AP. That is, the AP can specify the repetition frequency of the limited service period. This allows the AP to avoid transmitting the TWT element of the beacon frame every time to establish the limited service period. In this case, the service period period can be set according to the characteristics of the low-latency service in which low-latency traffic is used. For example, the period of a low-latency service period in which low-latency traffic is generated every 50 ms can be 50 ms.

[0138] Additionally, a quiet interval can be set for stations that do not support limited TWT. In conventional wireless LANs, a quiet interval is a period to support channel sensing. When a quiet interval is set, all stations stop transmitting. This quiet interval characteristic can be utilized to protect the limited service period. This is explained in detail in Figure 26. In this case, stations that do not support limited TWT can be limited to legacy stations.

[0139]

[0140] FIG. 11 shows an AP setting a quiet interval according to an embodiment of the present invention.

[0141] An AP operating a restricted TWT can establish a quiet period by transmitting a Quiet element. During the Quiet period, stations suspend channel access. However, if channel access of stations participating in the restricted TWT is restricted, low-latency traffic cannot be transmitted. Therefore, stations participating in the restricted TWT can ignore the Quiet period corresponding to the restricted service period. In this case, the Quiet period corresponding to the restricted service period represents a Quiet period established to protect the restricted service cycle of the restricted TWT. Specifically, stations participating in the restricted TWT can regard the Quiet period corresponding to the restricted service period as a restricted service period. An AP operating a restricted TWT may not set the Quiet period to match the restricted service period. This is because the Quiet period in the Quiet element is set in units of TU (time units, 1024us), while the TWT is set in units of 256us.

[0142] However, if channel access is performed in a quiet interval that is not set for a limited service period, it may interfere with a quiet interval that is not set for a limited service period. Therefore, it is necessary to distinguish between a quiet interval set for a limited service period, i.e., a quiet interval corresponding to a limited service period. Therefore, a station participating in a limited TWT may not be able to ignore a quiet interval that does not correspond to a limited service period. A station may not be able to perform any transmission in a quiet interval that does not correspond to a limited service period. Specifically, a station participating in a limited TWT may not be able to ignore a quiet interval that does not overlap with a limited service period. In a specific embodiment, a station participating in a limited TWT may not be able to perform any transmission in a quiet interval that does not overlap with a limited service period.

[0143] Additionally, in the above embodiments, a station participating in a limited TWT may consider a quiet interval corresponding to a limited service period if the start time of the limited service period and the start time of the quiet interval are within a predetermined time, and if the start time of the service period and the start time of the quiet interval are within a predetermined time. As described above, an AP operating a limited TWT may not set the quiet interval to match the limited service period.

[0144] In the embodiment of Fig. 11, the AP transmits a beacon frame to establish a quiet period and a restricted service period. In Fig. 11(a), the quiet period is set to the same time period as the restricted service period. Therefore, stations participating in the restricted TWT in the quiet period perform channel access. In Fig. 11(b), the quiet period is set to a time period starting from a time earlier than the start time of the restricted service period to a time later than the end time of the restricted service period. In Fig. 11(b), channel access of stations participating in the restricted TWT in the quiet period that does not overlap with the restricted service period is restricted. Stations participating in the restricted TWT in the quiet period that overlaps the restricted service period perform channel access.

[0145]

[0146] As previously explained, channel access may be restricted during limited service periods. Accordingly, these restrictions may also apply to TXOP settings. This is explained in Figure 12.

[0147] FIG. 12 illustrates a method for setting a TXOP by considering a limited service period of a station according to an embodiment of the present invention.

[0148] A station that has acquired a TXOP before the start of a restricted service period, i.e., a TXOP holder, may need to terminate the TXOP before the start of the restricted service period. This is because if frame exchange of the TXOP holder continues even after the start of the restricted service period, transmission of low-latency traffic may be interrupted. In this case, the station may be a non-legacy station. In another specific embodiment, the station may be limited to stations that support restricted TWT. That is, this restriction may not be applied to stations that set the value of the dot11RestrictedTWTOptionImplemented field to false.

[0149] In a specific embodiment, if a station that is a TXOP holder transmits low-latency traffic, it may continue to exchange frames even after the limited service period begins.

[0150] Describes the specific method by which a station terminates a TXOP before the limited service period.

[0151] A station can set a TXOP based on a limited service period. Specifically, the station can set the TXOP end time to be before the start of the limited service period. At this time, the station can set the duration of the initiating frame that initiates the frame exchange sequence to be before the start of the limited service period. For example, if the station successfully accesses the channel 3 ms before the start of the limited service period, the station can set the TXOP to be 3 ms before. Additionally, the station can end the TXO by transmitting a CTS-to-Self frame. At this time, the station can transmit the CTS-to-Self frame at the default transmission rate, 6 Mbps. This is because many legacy stations can receive the frame when the station transmits the frame at the default transmission rate.

[0152] In another specific embodiment, a station may transmit a CF-End frame before the start of a limited service period. This allows the station to terminate a TXOP before the start of the limited service period. In this case, the station may transmit the CF-End frame at the default transmission rate of 6 Mbps. This is because when a station transmits a frame at the default transmission rate, many legacy stations may receive the frame.

[0153] In addition, a station that is not a TXOP holder may release the NAV set before the start of the restricted service period at the start of the restricted service period. At this time, the station may be a station that supports restricted TWT. That is, the station may be a station that sets the value of the dot11RestrictedTWTOptionImplemented field to True. A station that is not a TXOP holder but does not support restricted TWT may not release the NAV set before the start of the restricted service period at the start of the restricted service period. However, if the station completes the frame exchange and the remaining duration of the TXOP is less than twice the sum of the time required to transmit the CF-End frame and SIFS, the station may not transmit the CF-End frame. At this time, the station may consider the TXOP to be released at the start of the restricted service period. Specifically, the station may consider the basic NAV to be released at the start of the restricted service period.

[0154] In another specific embodiment, stations may be limited to those participating in a limited TWT.

[0155] In the embodiment of FIG. 12, the AP transmits a beacon frame including a TWT element to signal that a restricted service period is established. In the embodiment of FIG. 12(a), the station transmits an RTS frame to establish a TXOP. At this time, the station sets the value of the duration field of the RTS frame to before the restricted service period. The station performs a frame exchange with the AP and completes the frame exchange before the start of the restricted service period. At this time, the station transmits a CTS-to-Self frame last. In the embodiment of FIG. 12(b), the station transmits an RTS frame to establish a TXOP. At this time, the station sets the value of the duration field of the RTS frame without considering the restricted service period. The station performs a frame exchange with the AP and completes the frame exchange before the start of the restricted service period. At this time, the station releases the TXOP by transmitting a CF-end frame last.

[0156] In conventional wireless LAN operation, operations that can be transmitted beyond the TXOP limit are defined as exceptions to the TXOP rule. For example, retransmission of a single MPDU, transmission of a single MSDU (not included in an A-MSDU and an A-MPDU composed of two or more MPDUs) under a block ack agreement, transmission of control frames and QoS Null frames (not included in an A-MPDU composed of two or more MPDUs) can be transmitted beyond the TXOP limit. If such exceptions are recognized even for a limited service period, transmission of low-latency traffic may be delayed. Such exceptions to the TXOP limit cannot be applied because they violate the limited service period.

[0157] If the end time of a TXOP is within a predetermined time difference from the start time of the limited service period, the station may determine that the TXOP is a TXOP acquired before the start of the limited service period. The predetermined time may be 100 us. In another specific embodiment, if the end time of a TXOP is within the limited service period, the station may determine that the TXOP is a TXOP acquired before the start of the limited service period.

[0158]

[0159] As previously explained, a station may need to complete frame exchanges before the limited service period begins. Accordingly, a station may not be permitted to initiate frame exchanges if the completion time of the frame exchange falls within the limited service period. In this case, the station can perform fragmentation to complete the frame exchange before the start of the limited service period.

[0160] Additionally, if a station that is a TXOP holder transmits low-latency traffic in a frame exchange performed by the station, the station may continue to exchange frames even after the low-latency service period begins.

[0161]

[0162] The channel access procedure considering the limited service period is explained through Fig. 13.

[0163] FIG. 13 shows a station performing a channel access procedure again considering a limited service period according to an embodiment of the present invention.

[0164] As previously explained, even if a station completes channel access before the limited service period, if the frame exchange is completed after the start of the limited service period, the station may initiate the channel access procedure again without performing transmission. At this time, the station may reacquire the value of the backoff counter. At this time, the station may use the same size of the CW used in the previous channel access procedure. That is, the station may not double the size of the CW used in the previous channel access procedure, nor may it initialize it to the minimum value that the CW can have. In addition, the station may not increase the number of retries, such as the QSRC (QoS STA Retry Counter).

[0165] Additionally, if the time at which the station completes channel access is within a pre-specified time from the start of the limited service period, the station may initiate the channel access procedure again without performing transmission.

[0166] In the preceding embodiments, a station attempting to transmit low-latency traffic may initiate frame exchange after channel access is completed, even if the frame exchange completion time is after the start of a restricted service period. This exception may only be permitted if the station attempting to transmit low-latency traffic is participating in a restricted TWT.

[0167] Additionally, as previously described, a station can operate as if an NAV is set for ACs for traffic other than low-latency traffic. Therefore, the station can determine that the CCA result for transmission of ACs for traffic other than low-latency traffic is not idle (BUSY).

[0168] In the embodiment of FIG. 13, the AP transmits a beacon frame containing a TWT element to signal that a limited service period is established. Before the limited service period begins, the backoff counter value of the station's channel access reaches 0. The station determines that the completion time of the frame exchange containing the traffic to be transmitted is after the start time of the service period. Therefore, the station acquires a backoff counter within the CW value used in the previous channel access procedure. The station performs the channel access procedure again using the acquired backoff counter. At this time, the station does not increment the retransmission counter.

[0169]

[0170] All low-latency traffic transmission may be completed before the limited service period ends. In such cases, limiting the transmission of non-low-latency traffic due to the low-latency service period may be inefficient. Therefore, a method for terminating the limited service period early may be necessary. This is described in the example of FIG. 29.

[0171] FIG. 14 illustrates an operation of an AP terminating a limited service period early according to an embodiment of the present invention.

[0172] In order for an AP to terminate a limited service period early, it must be able to determine that all low-latency traffic transmissions by a station participating in the limited TWT have been completed. To this end, a station participating in the limited TWT can signal whether to transmit additional low-latency traffic in the frame it transmits. Specifically, a station can signal that it will transmit additional low-latency traffic by setting the value of the More data subfield of the Frame Control field of the frame. In this case, if the value of the More data subfield of the Frame Control field of a frame transmitted in the limited service period is 1, the More data subfield indicates that additional low-latency traffic is required and may not indicate whether additional transmission of traffic other than low-latency traffic is required. For example, if a station participating in the limited TWT does not store low-latency traffic in its transmission buffer and only stores non-low-latency traffic, the station can set the value of the More data subfield of the Frame Control field of the frame it transmits in the limited service period to 0. An AP may prematurely terminate a restricted service period based on whether a station participating in a restricted TWT has a non-zero value in the More data subfield of the Frame Control field of a frame in the restricted service period. Specifically, if there is no low-latency traffic to transmit in the AP's transmit buffer and a station participating in a restricted TWT has a non-zero value in the More data subfield of the Frame Control field of a frame in the restricted service period, the AP may prematurely terminate the restricted service.

[0173] An AP can terminate a limited service period early by transmitting a pre-designated control frame. The control frame may be a CF-End frame. In this case, the AP can set the BSSID (TA) field of the CF-End frame to the AP's MAC address or BSSID. Additionally, the AP can set the Individual / Group bit of the BSSID (TA) field of the CF-End frame to 1. In another specific embodiment, the AP can terminate a limited service period early by transmitting a pre-designated management frame.

[0174] A station that receives a pre-designated frame that terminates the limited service period within a limited service period can determine that the limited service period has ended. At this time, the station that received the pre-designated frame can resume channel access without the restrictions applied to the limited service period. As described above, the pre-designated frame may be a CF-End frame. At this time, if the value of the TA (BSSID) field of the CF-End frame received by the station within the limited service period is the MAC address of the AP to which the station is associated, the station can determine that the CF-End frame is the CF-End frame that terminates the limited service period.

[0175] As previously explained, a quiet interval can be set for the limited service period to protect the limited service period from legacy wireless communication terminals. At this time, the AP can transmit a CF-End frame to end the limited service period. This is because when the AP transmits a CF-End frame, it can also release the quiet interval set for the legacy station.

[0176] In the embodiments described above, the CF-End frame may have a Frame Control field whose Type is a control frame (Type value B3 B2 == 01) and whose Subtype is a CF-End frame (Subtype value B7 B6 B4 B4 == 1110).

[0177] When a quiet interval is set for a restricted service period, a station participating in the restricted TWT may not be permitted to transmit a CF-End frame within the restricted service period. In a specific embodiment, a station participating in the restricted TWT may not be permitted to transmit a CF-End frame in the quiet interval corresponding to the restricted service period. This is because when a station participating in the restricted TWT transmits a CF-End frame, the NAV set for the legacy station is released. However, if the CF-End frame is used to terminate the restricted service period early as described above, the AP may transmit the CF-End frame within the restricted service period.

[0178] In the embodiment of FIG. 14, the AP transmits a beacon frame including a TWT element and a Quiet element. A station supporting restricted TWT determines that a restricted service period has been set, and a station not supporting restricted TWT determines that a quiet period has been set. If the AP determines that transmission of all low-latency traffic within the restricted service period has been completed, the AP transmits a CF-End frame to early end the restricted service period and releases the quiet period set for legacy stations. At this time, the station supporting restricted TWT determines that the channel access restriction applied during the restricted service period has been removed. Specifically, if the embodiment in which the NAV is set during the restricted service period as described above is applied, the station supporting restricted TWT can determine that the NAV for the restricted service period has been released. In addition, a station not supporting restricted TWT that has received the CF-End frame releases its NAV.

[0179]

[0180] <TID Restrictions in Limited TWT>

[0181] As discussed above, a TWT SP can be configured so that the AP allows transmission of traffic with specific conditions, and restricts transmission of traffic without specific conditions. In this case, the AP transmits information related to the TID corresponding to traffic with specific conditions (e.g., information indicating the TID corresponding to traffic satisfying the specific conditions), and a non-AP STA can transmit and receive traffic corresponding to the TID transmitted from the AP within the TWT SP. In this case, the specific conditions may be conditions related to transmission delay of traffic (e.g., low-latency traffic), and transmission of traffic without the specific conditions may be restricted. Restricted transmission may mean that transmission is not possible during the TWT SP, transmission is possible under certain restrictions (e.g., transmission combined with MPDUs of traffic corresponding to TIDs that satisfy certain conditions, transmission combined with MPDUs of traffic corresponding to TIDs that satisfy certain conditions within a certain interval set within the TWT SP, etc.), or channel access through the EDCAF of ACs corresponding to TIDs that are not indicated by the AP is restricted.

[0182] Alternatively, the configured R-TWT SP may be reconfigured into multiple sections, and in at least one specific section, only traffic for a TID corresponding to traffic with a specific condition may be transmitted, and in sections other than at least one specific section, traffic for a TID corresponding to traffic that does not have the specific condition may be allowed to be transmitted under limited conditions (or specific restrictions). For example, if the R-TWT SP is configured with a first section and a second section, in the first section, only traffic for a TID corresponding to traffic with a specific condition (e.g., low latency, etc.) may be transmitted, and in the second section, traffic for a TID corresponding to traffic that does not have the specific condition may be allowed to be transmitted under limited conditions (or specific restrictions).

[0183] Information related to the TID may be transmitted in a bitmap format, where each bit may indicate a specific TID, and may be included in a trigger frame or a user information field containing information about each terminal in the trigger frame.

[0184] For example, if a Restricted TWT SP (hereinafter, R-TWT SP) that can only transmit low-latency traffic is set, each STA may be allowed to transmit only low-latency traffic within the R-TWT SP section, and may be restricted from transmitting traffic other than low-latency traffic. At this time, the types of traffic that STAs may transmit within a specific R-TWT SP may be restricted to traffic corresponding to TIDs indicated by the AP. That is, the AP may set TIDs of traffic that can be transmitted during the R-TWT SP during the process of setting up the R-TWT SP, and may notify the STAs of the set TIDs. In this case, non-AP STAs may only transmit traffic corresponding to the TIDs indicated by the AP within the R-TWT SP, and may be restricted from transmitting traffic corresponding to TIDs that are not indicated by the AP.

[0185] Hereinafter, low-latency traffic may refer to latency-sensitive traffic, traffic whose transmission time must be within a certain time, or traffic whose transmission time is subject to specific conditions.

[0186] An AP can indicate information related to TIDs that can be transmitted within an R-TWT SP through a TWT element transmitted to establish an R-TWT SP. If the AP indicates specific TIDs through a TWT element transmitted to establish a specific R-TWT SP, the AP and STAs may be able to transmit only traffic corresponding to the specific TIDs within the specific R-TWT SP. At this time, transmission of traffic corresponding to TIDs other than the specific TIDs may be restricted. At this time, traffic (MPDU, MSDU, etc.) corresponding to the other TIDs may be transmitted only in a form aggregated (e.g., A-MPDU) through a PPDU in which frames corresponding to the specific TIDs are transmitted.

[0187] FIG. 15 illustrates an example of a TWT element for setting a broadcast TWT SP (Target Wake Time Service Period) according to an embodiment of the present invention.

[0188] Referring to FIG. 15, the AP can set a specific section as an R-TWT SP to allow transmission of only traffic having the specific conditions described above, and can transmit a TWT element to transmit information of the set R-TWT SP.

[0189] Specifically, the broadcast TWT parameter set field may mean one or more parameter set fields included in the TWT parameter information field of the TWT element when the Negotiation Type subfield (of the Control field) of the TWT element indicates that it is a broadcast TWT.

[0190] Referring to (a) of FIG. 15, the Broad TWT Parameter Set field may include a Restricted TWT Traffic Info field. The Restricted TWT Info field indicates information about TIDs to be considered as low-latency traffic in the R-TWT SP configured through the corresponding TWT element, which will be described in more detail with reference to an embodiment of FIG. 16 described below. In this way, the Broadcast TWT Parameter Set field may have a configuration including or not including the Restricted TWT Traffic Info field. Accordingly, an STA (AP, non-AP STA) that has received the TWT element must be indicated whether the Broadcast TWT Parameter Set field includes the Restricted TWT Traffic Info field. That is, the TWT element must include information indicating that the configured TWT SP is an R-TWT SP, which is a TWT SP for traffic with specific conditions (e.g., low-latency traffic), and / or information indicating whether the TWT element includes a traffic information field related to the R-TWT SP.

[0191] Whether the broadcast TWT information field includes a restricted TWT traffic information field can be indicated through the broadcast TWT information field. More specifically, the broadcast TWT information field (see FIG. 15(b)) can include a restricted TWT traffic information present subfield. If the restricted TWT traffic information present subfield is indicated as 1, the broadcast TWT information field including the restricted TWT traffic information present subfield can have a configuration including the restricted TWT traffic information field. Conversely, if the restricted TWT traffic information present subfield is set to 0, the broadcast TWT information field including the restricted TWT traffic information present subfield can have a configuration not including the restricted TWT traffic information field. In this case, the restricted TWT traffic information present subfield can be included only in the broadcast TWT parameter set field transmitted to establish an R-TWT SP. That is, only the broadcast TWT parameter set field corresponding to the R-TWT can have the restricted TWT traffic information present subfield set to 1. At this time, the STA transmitting the TWT element to establish the R-TWT SP may be the AP scheduling the R-TWT SP.

[0192] FIG. 16 illustrates an example of a restricted TWT traffic information field for setting a restricted TWT SP according to an embodiment of the present invention.

[0193] Referring to Fig. 16(a), the restricted TWT traffic information field may include a traffic information control field, a restricted TWT DL TID Bitmap field, and a restricted TWT UL TID Bitmap field. The traffic information control field (see Fig. 16(b)) may include a DL(UL) TID Bitmap Valid and UL TID Bitmap Valid subfields. If the DL(UL) TID Bitmap Valid subfield is indicated as 0, it may mean that the restricted TWT DL(UL) TID Bitmap subfield is reserved and traffic corresponding to all TIDs is considered low-latency traffic. That is, if the DL(UL) TID Bitmap Valid subfield is indicated as 0, DL(UL) traffic transmitted within the R-TWT SP is not subject to restrictions related to TID.

[0194] Meanwhile, if the DL(UL) TID Bitmap Valid subfield is set to 1, only the TIDs corresponding to the bits set to 1 in the restricted TWT DL(UL) TID Bitmap subfield can be considered as low-latency traffic. More specifically, if the kth bit of the DL(UL) TID Bitmap subfield is set to 1, the downlink (uplink) traffic corresponding to the downlink (uplink) TID k can be considered as low-latency traffic, and if the nth bit is set to 0, the traffic corresponding to the TID n can be considered as not low-latency traffic. Therefore, the traffic for the TID corresponding to the bit set to '1' in the DL(UL) TID Bitmap subfield can be recognized as traffic having a specific condition, and can be transmitted within the set R-TWT SP.

[0195] At this time, the restricted TWT DL / UL Bitmap subfield may be included in the restricted TWT traffic information field only when the DL / UL Bitmap Valid subfield of the traffic information control field is indicated as 1. That is, the restricted TWT traffic information field in which the DL TID Bitmap Valid subfield is indicated as 0 may have a configuration that does not include the restricted TWT DL TID Bitmap subfield. In the description and embodiments of the present invention described below, for the convenience of description, a TID indicated to be considered as low-delay traffic is referred to as a low-delay TID.

[0196] If, in the restricted TWT traffic information field corresponding to a specific R-TWT SP, the UL TID Bitmap subfield is indicated as 1 and the restricted TWT UL TID Bitmap subfield is indicated as 00001111, the specific R-TWT SP may be an R-TWT SP that indicates only TID 4 to TID 7 as low-latency TIDs for the UL direction. In this case, when scheduled STAs transmit UL traffic within the R-TWT SP, they may only transmit traffic corresponding to TID 4 to TID 7. At this time, traffic corresponding to the remaining TIDs (TID 0 to TID 3) excluding TID 4 to TID 7 may be restricted from transmission. At this time, the restriction of transmission may mean that transmission (TXOP) cannot be initiated (obtained) through the EDCAF of the AC (Access Category, Access Class) corresponding to TID 0 to TID 3. Channel access restrictions related to TID are described in more detail through embodiments of the present invention described below.

[0197]

[0198] As described above, the broadcast TWT parameter set field transmitted to establish an R-TWT SP has a configuration including a restricted TWT traffic information Present subfield as considered in one embodiment of FIG. 15. At this time, the restricted TWT traffic information Present subfield may be indicated (included) only when the corresponding broadcast TWT parameter set field is transmitted to establish an R-TWT SP. In other words, if the broadcast TWT parameter set field is not for establishing an R-TWT SP, the broadcast TWT parameter set may have a configuration that does not include the restricted TWT traffic information Present subfield. That is, the restricted TWT traffic information Present subfield illustrated in FIG. 15(b) may be reserved. In this way, the broadcast TWT parameter set field transmitted to establish a broadcast TWT SP other than an R-TWT SP and the broadcast TWT parameter set field transmitted to establish an R-TWT SP may have different formats. Therefore, an STA receiving a broadcast TWT parameter set field must know whether the broadcast TWT parameter set field is transmitted to establish an R-TWT SP or not.

[0199] Therefore, an STA transmitting a broadcast TWT parameter set field to establish an R-TWT SP can indicate whether the corresponding broadcast TWT parameter set field is for establishing an R-TWT SP through a Request Type field of the broadcast TWT parameter set field. More specifically, an STA transmitting a broadcast TWT parameter set field to establish an R-TWT SP can indicate that the corresponding broadcast TWT parameter set field has a format related to R-TWT by setting a value of a broadcast TWT Recommendation field included in a Request Type field of the broadcast TWT parameter set field to a specific value (e.g., 4).

[0200] Additionally, an STA transmitting a broadcast TWT parameter set field for establishing an R-TWT SP may set a value of a broadcast TWT Recommendation field to indicate information regarding restrictions on TIDs that can be transmitted within the R-TWT SP to be established.

[0201]

[0202] The TWT elements transmitted / received by 11ax STAs may include a Broadcast TWT Recommendation field. The Broadcast TWT Recommendation field is used to indicate the types of frames to be transmitted during the established Broadcast TWT SP and restrictions related to the characteristics of the Broadcast TWT SP. The following is how 11ax STAs (APs and non-AP STAs) utilize the Broadcast TWT Recommendation field values ​​0 to 3.

[0203] The Broadcast TWT Recommendation field, when set to 0, may be interpreted / indicated to mean that this is a Broadcast TWT SP with no restrictions on the frames it transmits.

[0204] The Broadcast TWT Recommendation field, when set to a value of 1 or 2, may be interpreted to indicate / mean that the TWT scheduled STA is a broadcast TWT SP recommended to request only certain types of status, feedback.

[0205] The Broadcast TWT Recommendation field, when set to a value of 3, indicates / can be interpreted to mean that the AP is a broadcast TWT SP that must transmit a TIM frame or a FILS Discovery frame containing a TIM element at the beginning of every TWT SP, although there are no restrictions on the frames it transmits.

[0206]

[0207] An R-TWT SP can be considered a type of broadcast TWT SP, and the value of the broadcast TWT Recommendation field can indicate whether it is an R-TWT SP and whether frame transmission restrictions are applied to the R-TWT SP. In this case, a method for applying frame transmission restrictions to an R-TWT SP may be to limit the TID of the traffic being transmitted to a specific TID. In this case, the specific TID may be a low-latency TID.

[0208]

[0209] For example, if the value of the broadcast TWT Recommendation field transmitted in relation to a specific R-TWT SP is indicated as a specific value (e.g., 5), the specific R-TWT SP may be restricted to transmit only low-latency TIDs. In this case, MPDUs of TIDs other than low-latency TIDs may not be allowed to be transmitted in aggregate with low-latency traffic. That is, if the value of the broadcast TWT Recommendation field is set to a specific value, TIDs that are not indicated as low-latency TIDs may have their channel access through the corresponding EDCAF restricted, and their aggregation with low-latency traffic restricted, thereby making them impossible to be transmitted within the R-TWT SP. That is, if the value of the broadcast TWT Recommendation field is set to a specific value, MPDUs that do not correspond to low-latency TIDs cannot be transmitted within the R-TWT SP. This can be understood as applying MPDU transmission (or MPDU aggregation) restrictions together with restrictions on (AC's) EDCAF that do not correspond to low-latency TIDs. In the present invention, the corresponding R-TWT SP is named a TID-restricted-TWT (TID-R-TWT) SP.

[0210] When the value of the Broadcast TWT Recommendation field is indicated as a specific value, the Restricted TWT Traffic Information Present subfield, the DL / UL TID Bitmap Valid subfields (or at least one of the subfields) may always be set to 1. This may be because transmission restrictions on traffic of non-low-latency TIDs may be applied only when a low-latency TID is specified.

[0211] As another example, if the value of the broadcast TWT Recommendation field transmitted in relation to a specific R-TWT SP is indicated by another specific value (e.g., 4), the specific R-TWT SP may be restricted so that low-latency TIDs can be transmitted preferentially. That is, within the configured R-TWT SP, traffic with specific conditions (e.g., low latency) may be transmitted with priority over other traffic, and other traffic may be transmitted under restricted conditions.

[0212] For example, a restrictive condition may mean that transmission is not allowed, is transmitted in combination with traffic having certain conditions, or is transmitted alone or in combination with traffic having certain conditions only in certain sections of the R-TWT SP. Alternatively, non-low-latency TID traffic (frame, MPDU, packet, etc.) may be transmitted in the R-TWT SP only when there is no more low-latency TID traffic to be transmitted. For example, the EDCAF corresponding to non-low-latency TIDs may be restricted to perform channel access only when the Transmission queue of the AC corresponding to the low-latency TIDs is empty. As another example, a frame (MPDU) corresponding to a non-low-latency TID may be restricted to be aggregated into the A-MPDU of the low-latency traffic only when the Transmission queue of the AC corresponding to the low-latency TID is empty. That is, the case where a Multi-TID A-MPDU includes an MPDU of a TID other than a low-latency TID may be limited to when there are no more frames for low-latency TIDs.

[0213] As another example, it is possible to implicitly indicate / determine whether only low-latency TID transmission is allowed in a specific R-TWT SP, or whether non-low-latency TID traffic is also allowed to be transmitted with restrictions. More specifically, whether only low-latency TID transmission is allowed in a specific R-TWT SP can be indicated / determined based on whether the duration of the R-TWT SP exceeds a specific length.

[0214] In this case, if the length of the R-TWT SP is shorter than a specific value (a pre-promised value), the R-TWT SP may be designated / determined as an R-TWT SP that transmits only frames of low-delay TID. Accordingly, a non-AP STA that is a member of an R-TWT SP whose length is shorter than (or less than) a specific value must transmit only frames of low-delay TID within the R-TWT SP.

[0215] On the other hand, a non-AP STA that is a member of an R-TWT SP whose length is longer than (exceeds) a certain value may first transmit a low-delay TID frame within the R-TWT SP, and then transmit a TID frame other than a low-delay TID.

[0216] At this time, a non-AP STA that is a member of an R-TWT SP whose length is longer than a specific value (e.g., 1 TU) must transmit only frames of a low-delay TID before the elapsed time of the R-TWT SP reaches the specific value, and if the elapsed time of the R-TWT SP exceeds the specific value, it can transmit frames of a TID other than the low-delay TID during the remaining R-TWT SP period.

[0217] That is, it is possible for the operation method of the R-TWT SP to be determined / instructed / changed depending on the length of the R-TWT SP. In this way, in cases where the operation method is applied differently for each time section within a single R-TWT SP (i.e., there are sections where only low-latency TID frame transmission is allowed and sections where frame transmission of TIDs other than low-latency TID is also allowed), the Broadcast TWT Recommendation field of the TWT element transmitted when establishing the R-TWT SP can be set to a specific value.

[0218] If a specific R-TWT SP is established with the Broadcast TWT Recommendation field indicated with a specific value, and another R-TWT SP is established with the Broadcast TWT Recommendation field indicated with a different value, only the specific R-TWT SP established with the specific value indicated may be an R-TWT SP for which the operation policy changes within the R-TWT SP period. For example, if the Broadcast TWT Recommendation field of the TWT element transmitted when establishing the R-TWT SP is set to a specific value (e.g., 5), the R-TWT SP established by the corresponding TWT element may have different operation methods applied to each time period. In this case, if the Broadcast TWT Recommendation field of the TWT element transmitted when establishing the R-TWT SP is set to a different value (e.g., 4), the R-TWT SP established by the corresponding TWT element has the same operation method applied to all time periods corresponding to the R-TWT SP. At this time, the operating method refers to the operating method (channel access and frame transmission method) related to whether only frame transmission of low-latency TID is allowed or frame transmission of other TIDs is allowed with restrictions.

[0219] In addition, it is possible that only low-latency TID frame transmission is allowed within a single R-TWT SP, and then frame transmission of another TID is allowed, that is, the operation method of the R-TWT SP can be changed according to a method agreed upon in advance during the operation of the R-TWT SP. In this case, the AP can perform signaling for changing the operation method during the R-TWT SP section. Alternatively, the operation method of the R-TWT SP may be changed according to a pre-agreed rule. The method for changing the transmission rule related to the low-latency TID within the R-TWT SP according to a pre-agreed method during operation is described in more detail through embodiments of the present invention described below, and thus a detailed description thereof is omitted. The frame transmission rule for a situation in which the operation method is changed within a single R-TWT SP (including both a case in which the operation method is changed by a method for setting an R-TWT SP or a case in which the operation of the R-TWT SP is changed through a pre-agreed method) is described through an embodiment of FIG. 22.

[0220] Alternatively, the value of the Broadcast TWT Recommendation field may be one type of value indicating that it is R-TWT, and whether or not to restrict the TID may be indicated in each trigger frame.

[0221] For example, if the broadcast TWT Recommendation field value is set to 4 and there is an established R-TWT SP, a trigger frame transmitted to the R-TWT SP may indicate whether or not a TID is restricted. At this time, the trigger frame may have a configuration including a 1-bit subfield indicating whether or not a TID is restricted. If 1 bit indicating whether or not a TID is restricted is set to 1, a TB PPDU responded through the trigger frame may be restricted to include only MPDUs for low-latency TIDs in the TB PPDU, like a TB PPDU transmitted in the TID-R-TWT described above. On the other hand, if 1 bit indicating whether or not a TID is restricted is set to 0, a TB PPDU responded through the trigger frame may include MPDUs for TIDs other than low-latency TIDs through combining, etc.

[0222] The low-latency TID-related transmission restrictions applied within the aforementioned R-TWT SP may take precedence over the (multi-TID) A-MPDU aggregation rules. That is, while among the A-MPDU aggregation rules, an MPDU corresponding to an AC with a higher priority than the AC of a specific EDCAF that is a TXOP holder may be aggregated into an A-MPDU, an A-MPDU transmitted within an R-TWT SP may not be aggregated into an A-MPDU even if the MPDU corresponds to an AC with a higher priority than the AC of the EDCAF if it is not traffic (MPDU) of a low-latency TID. Similarly, an MPDU corresponding to an AC with a higher priority than the Preferred AC indicated through a trigger frame may be included in a TB PPDU in the form of a multi-TID A-MPDU, while among the multi-TID A-MPDUs transmitted within an R-TWT SP, an MPDU corresponding to a TID other than the low-latency TID may not be included in a multi-TID A-MPDU.

[0223] If there are no more MPDUs corresponding to the low-latency TID, the Scheduled STA may set the More Data subfield of the frame included in the last PPDU it transmits to 1 to inform the Scheduling AP that there is no more low-latency traffic to transmit.

[0224] FIG. 17 illustrates values ​​of fields included in a Broadcast TWT Parameter Set field according to an embodiment of the present invention.

[0225] The broadcast parameter set information field transmitted to establish an R-TWT SP can indicate information related to the R-TWT SP using the broadcast TWT Recommendation subfield value of the Request Type field.

[0226] Referring to FIG. 17, when the value of the broadcast TWT Recommendation subfield is set to 4, it can be understood that this indicates / interprets that the corresponding broadcast TWT SP is an R-TWT SP. In addition, even when the value of the broadcast TWT Recommendation subfield is set to 5, it can be determined that this indicates / interprets that the corresponding broadcast TWT SP is an R-TWT SP. However, two broadcast TWT Recommendation subfield values ​​indicating an R-TWT SP may be R-TWT SPs that have different restrictions on frames transmitted within the R-TWT SP. In this case, the restrictions on frames transmitted within the R-TWT SP may be restrictions related to the TID of the transmitted MPDU. More specifically, two R-TWT SPs indicated by the two different values ​​may be R-TWT SPs that apply different rules to the TID of transmittable MPDUs.

[0227] For example, an R-TWT SP whose broadcast TWT Recommendation field is indicated as 4 may be an R-TWT SP that is proposed to transmit low-latency traffic and may be an R-TWT SP that is restricted from transmitting MPDUs corresponding to TIDs other than low-latency TIDs. In this case, traffic other than low-latency traffic may be transmitted only when low-latency traffic is transmitted or when there is no low-latency traffic to transmit.

[0228] For example, a TID-R-TWT SP with a value of 5 in the Broadcast TWT Recommendation field is an R-TWT SP that only allows transmission of low-latency traffic, and traffic other than low-latency traffic must not be transmitted.

[0229] Therefore, if the value of the broadcast TWT Recommendation field received from the scheduling AP is indicated as 4, the scheduled STA can recognize that the broadcast TWT corresponding to the broadcast TWT Recommendation field is R-TWT. In this case, the scheduled STA can transmit MPDUs of low-latency TIDs in the R-TWT with priority and transmit MPDUs of TIDs other than low-latency TIDs in a limited manner.

[0230] Additionally, if the value of the broadcast TWT Recommendation field received from the scheduling AP is indicated as 5, the scheduled STA may recognize that the broadcast TWT corresponding to the broadcast TWT Recommendation field is a TID-R-TWT with a TID restriction. In this case, the scheduled STA may only transmit MPDUs of low-latency TIDs within the TID-R-TWT.

[0231] <R-TWT SP의 설정>

[0232] When a non-AP STA wishes to request the setting of a TWT SP, it may transmit a request message requesting the setting of a TWT SP to an AP STA. At this time, the request message may be transmitted including information indicating the type (or type) of the TWT SP for which the setting is requested. For example, when a non-AP STA requests the setting of an R-TWT SP, the non-AP STA may transmit a message requesting the setting of a TWT SP with a specific bit value set to '1' to request that the R-TWT SP be set. Thereafter, the AP STA may set a TWT SP according to the request of the non-AP STA, and then transmit information related to the set TWT SP by including it in a beacon frame or a management frame.

[0233] Specifically, a non-AP STA can request the AP to schedule an R-TWT SP by transmitting a TWT Request frame to the AP. At this time, the non-AP STA can transmit the TWT element (included in the TWT Request frame) that it transmits to request the R-TWT SP to the AP with the DL(UL) TID Bitmap Valid bit set to 1. This can be interpreted as a request for the non-AP STA to schedule an R-TWT SP considering the TIDs indicated by the restricted TWT DL(UL) TID Bitmap as low-latency TIDs. In this case, the AP may need to respond in the TWT Response frame with the restricted TWT DL(UL) TID Bitmap subfield set to be identical to the restricted TWT DL(UL) TID Bitmap subfield included in the TWT Request frame if the DL(UL) TID Bitmap Valid bit included in the TWT element of the received TWT Request frame is set to 1. In other words, when the Scheduling AP receives a request to schedule an R-TWT SP from a Scheduled STA, it may schedule an R-TWT SP that considers the TIDs indicated by the STA as low-latency TIDs.

[0234] <R-TWT SP의 운용>

[0235] According to the embodiments of the present invention described above, a broadcast TWT parameter set field transmitted to establish an R-TWT SP may have a configuration including a restricted TWT traffic information field. The restricted TWT traffic information field indicates information on TIDs that should be considered as low-latency traffic in the R-TWT SP to be established, and the Scheduled STA and / or Scheduling AP of the R-TWT SP performs traffic transmission based on the TID information indicated during the R-TWT SP establishment process. That is, the established specific R-TWT SP is an SP that always considers the same TIDs as low-latency TIDs even if the SP is repeated.

[0236] However, the traffic that each STA must process with low latency can be determined regardless of the TID. For example, traffic from an application processed by a specific STA may have characteristics that require low latency processing even though it is not video (AC_VI) or voice (AC_VO) data, and traffic from an application processed by another STA may not need to be processed with low latency even though it is video or voice data. In this way, the traffic that must be processed with low latency is determined according to the needs of each STA, and it may not be possible to classify it uniformly using information related to traffic type, such as TID. Therefore, each Scheduled STA may need to perform operations that consider different TIDs as low latency TIDs.

[0237] Furthermore, even within a single R-TWT SP, there may be cases where it is preferred to prioritize processing in a specific time interval as needed. For example, within a single R-TWT SP considering TIDs 4 to 7 as low-latency TIDs, a Scheduling AP may be scheduled to transmit a total of four trigger frames. In this case, the AP may prefer to receive only MPDUs corresponding to TID 7 via the TB PPDU responded to the first trigger frame, MPDUs corresponding to TID 6 in response to the second trigger frame, and MPDUs for TIDs 5 and 4 in response to the third and fourth trigger frames, respectively. In this case, the Scheduling AP needs to transmit the trigger frame and indicate information about the TIDs of the MPDUs it wants to receive in response to the trigger frame.

[0238] Accordingly, an AP that has set an R-TWT SP can transmit information for indicating a TID of traffic allowed to be transmitted in the set R-TWT SP by including it in a trigger frame. The information for indicating a TID of traffic allowed to be transmitted in the R-TWT SP can be included in a bitmap format, and each bit of the bitmap can indicate whether the corresponding TID is a TID for traffic allowed to be transmitted in the R-TWT SP. For example, when a bit of the bitmap is set to '0', the corresponding TID can be restricted from being transmitted within the set R-TWT SP, and when it is set to '1', the corresponding TID can be allowed to be transmitted within the set R-TWT SP.

[0239] Alternatively, information indicating the TID of traffic allowed to be transmitted in the configured R-TWT SP may be included in the user information field, which is information about each terminal in the trigger frame. In this case, the user information field may only contain information about one TID, and the TIDs in each user information field may be different TIDs.

[0240] Specifically, the Scheduling AP can indicate information about TIDs to be considered as low-latency TIDs in a TB PPDU responded to a trigger frame transmitted within the R-TWT SP. Scheduled STAs that are allocated RUs through a specific trigger frame and respond to a TB PPDU and Scheduled STAs that respond to a TB PPDU through an RA-RU must respond to a TB PPDU considering the TIDs indicated through the specific trigger frame as low-latency TIDs. In this case, responding to a TB PPDU considering a low-latency TID may mean limiting the TIDs of MPDUs included in a multi-TID A-MPDU transmitted through the TB PPDU to low-latency TIDs.

[0241] Information about the low-latency TID may be indicated only when the trigger frame is transmitted within the R-TWT SP. The subfield (bits) indicating the low-latency TID in the trigger frame transmitted within the R-TWT SP may be a reserved or other-purpose subfield in the trigger frame transmitted outside the R-TWT SP.

[0242] When the Scheduling AP indicates information about a low-latency TID through a trigger frame, it may need to indicate a TID only among the TIDs that the R-TWT SP to which the trigger frame is transmitted considers as a low-latency TID. That is, if the R-TWT SP considers TID 4 to TID 7 as a low-latency TID, the Scheduling AP may need to indicate a TID only among TID 4 to TID 7 when indicating a low-latency TID for a TB PPDU.

[0243] When information about a low-delay TID is indicated through a trigger frame, the Scheduled STA may need to operate based on the low-delay TID information indicated through the trigger frame when performing a TB PPDU response to the trigger frame. In other words, the Scheduled STA may need to respond to the TB PPDU based on the TID information indicated as a low-delay TID through the trigger frame, not the TID indicated as a low-delay TID in the R-TWT SP. In other words, if a specific TID indicated as a low-delay TID in the R-TWT SP is not indicated as a low-delay TID in the trigger frame, the MPDU of the specific TID may be restricted from being transmitted (responded to) through the TB PPDU. In this case, a TB PPDU response method considering a low-delay TID is omitted because it has been described through the embodiments of the present invention described above.

[0244] However, the low-latency TID indicated through the trigger frame may only be applied when the TB PPDU for that trigger frame is responded to.

[0245] FIG. 18 illustrates an example of a format of a trigger frame including information on a TID of traffic that can be transmitted in a limited TWT SP according to an embodiment of the present invention.

[0246] A trigger frame transmitted by a scheduling AP within an R-TWT SP may include a TID indicator in the Common Info field. More specifically, a TID Bitmap may be included. Each bit of the TID Bitmap corresponds to a different TID, and when a specific bit is set to 1, the TID corresponding to the specific bit may be indicated / interpreted as a low-latency TID.

[0247] Referring to FIG. 18, the Common Info field of the trigger frame may include a low-latency TID bitmap subfield. The low-latency TID bitmap subfield consists of 8 bits, and each of the 8 bits can be interpreted to correspond 1:1 to TID 0 to TID 7.

[0248] When a scheduling AP transmits a trigger frame within an R-TWT SP, it may attempt to receive a TB PPDU containing only MPDUs for specific low-latency TIDs from responding STAs (Scheduled STAs). In this case, the scheduling AP may indicate the specific low-latency TIDs through the low-latency TID Bitmap. At this time, the scheduling AP sets the bits (in the low-latency TID Bitmap) corresponding to the specific low-latency TIDs to 1.

[0249] When Scheduled STAs receive a trigger frame within an R-TWT SP, they may respond with a TB PPDU that includes only the MPDUs of the low-latency TIDs indicated in the trigger frame. In this case, Scheduled STAs may construct a (multi-TID) A-MPDU to be included in the TB PPDU, considering that the TIDs indicated in the low-latency TID Bitmap are low-latency TIDs.

[0250]

[0251] According to one embodiment of the present invention, a scheduling AP can indicate to each scheduled STA, through a trigger frame transmitted within an R-TWT SP, information on a TID to be considered as a low-delay TID in a TB PPDU responded to the trigger frame. Scheduled STAs that are allocated an RU through the trigger frame and respond to a TB PPDU must respond to the TB PPDU considering the TID indicated through the user information field included in the trigger frame (information related to its own AID is indicated through the AID12 subfield) as a low-delay TID. In this case, responding to the TB PPDU considering the low-delay TID may mean limiting the TIDs of MPDUs included in a multi-TID A-MPDU transmitted through the TB PPDU to low-delay TIDs. Alternatively, responding to the TB PPDU considering the low-delay TID may mean responding only to MPDUs corresponding to the TID indicated as the low-delay TID through the TB PPDU.

[0252] In this way, when indicating a low-latency TID through the user information field, the scheduling AP can indicate a different TID as the low-latency TID for each scheduled STA. Therefore, each scheduled STA can operate while recognizing a different TID as the low-latency TID even when receiving the same trigger frame within a specific R-TWT SP.

[0253] Information about a low-latency TID indicated in the user information field may have a form that directly indicates the ID of the TID rather than a TID bitmap. In other words, the low-latency TID indicated in the user information field may be limited to 1. This may be a signaling method considered because the bit margin that can be used to indicate a low-latency TID in the user information field is limited. However, if a specific TID is indicated as a low-latency TID through the user information field, a TID with a higher priority than the specific TID may be automatically determined (interpreted) as a low-latency TID. That is, if a specific TID is indicated as a low-latency TID in the user information field, not only the specific TID but also a TID with a higher priority than the specific TID may be indicated as a low-latency TID.

[0254] Similar to the low-latency TID indication using the Common Info field of the trigger frame described above, the low-latency TID indicated using the User Information field may also be valid only when a TB PPDU is responded to for the trigger frame containing the corresponding User Information field.

[0255] FIG. 19 illustrates an example of the format of a user information field of a trigger frame including information on a TID of traffic that can be transmitted in a limited TWT SP according to an embodiment of the present invention.

[0256] Referring to FIG. 19, the user information field of a trigger frame transmitted within an R-TWT SP may include an indicator for a low-latency TID. In one embodiment of FIG. 20, it is considered that the indicator for the low-latency TID is a low-latency TID subfield. The low-latency TID subfield may be a subfield included in a Trigger Dependent user information subfield of a user information field. In this case, the bit indicating the low-latency TID subfield may be a subfield indicated using a bit indicating the Preferred AC subfield in the user information field of a trigger frame transmitted outside an R-TWT SP.

[0257] The low-latency TID subfield indicates information about the TID that a Scheduled STA, which has been allocated an RU through the corresponding user information field and responds to a TB PPDU, should consider as a low-latency TID.

[0258] The operations performed by the STA performing frame exchange within the R-TWT SP described above, taking into account the low-latency TID, are as follows: 1) and 2).

[0259] 1) Operate on the TXOP you have acquired

[0260] An STA that acquires a TXOP within an R-TWT SP transmits a frame corresponding to a low-latency TID with priority. When an STA transmits a multi-TID A-MPDU, only frames corresponding to a low-latency TID can be aggregated in the multi-TID A-MPDU. At this time, when a frame corresponding to a low-latency TID is aggregated in a multi-TID A-MPDU, restrictions related to the TXOP limit of the Primary AC are not applied. More specifically, even if the TXOP limit of the Primary AC is 0, a frame of a low-latency TID corresponding to an AC other than the Primary AC can be included (aggregated) in the multi-TID A-MPDU. In addition, a frame of a low-latency TID corresponding to an AC with a lower priority than the Primary AC can also be included in the multi-TID A-MPDU. In other words, when a frame of a low-latency TID is included in a multi-TID A-MPDU, restrictions related to the priority of the AC are not applied.

[0261] If the STA no longer has a frame corresponding to the low-latency TID, i.e., if the frame corresponding to the low-latency TID is not in the transmission queue (of the EDCAF), the STA can transmit a frame other than the low-latency TID within the TXOP it has acquired. In this case, the frame other than the low-latency TID can be aggregated with the frame of the low-latency TID.

[0262] That is, it is possible for a single PPDU to contain frames of both low-latency TIDs and TIDs other than low-latency TIDs. In this case, the frames of the low-latency TID included in the single PPDU are positioned before the frames of the other TIDs included together.

[0263] In addition, the STA can also transmit a PPDU containing only frames of a TID other than the low-latency TID within the R-TWT SP, and the condition for the STA to transmit a PPDU containing only frames of a TID other than the low-latency TID may be that the frames of the low-latency TID no longer exist. In this case, the frames of the TIDs other than the low-latency TID may be aggregated according to the multi-TID A-MPDU configuration rules of the conventional Wi-Fi. More specifically, among the frames of the TIDs other than the low-latency TID, the frames corresponding to the AC with a higher priority than the Primary AC may be aggregated. That is, when the frame of the low-latency TID does not exist, the frames of the other TIDs that can be transmitted may be limited to the frames corresponding to the AC with a higher priority than the Primary AC. In this case, the frames corresponding to the same AC as the low-latency TID may be included (aggregated) in the PPDU transmitted within the R-TWT SP.

[0264] 2) Transmission behavior of TB PPDU in response to trigger frame

[0265] An STA that receives a trigger frame within an R-TWT SP and responds with a TB PPDU can determine which frames to include in the TB PPDU by considering the low-delay TID. More specifically, an STA that responds with a TB PPDU within an R-TWT SP must respond by including only frames of the TID indicated as the low-delay TID in the corresponding R-TWT SP in the TB PPDU. At this time, an STA that responds with a frame of the low-delay TID to the TB PPDU can respond with a multi-TID A-MPDU in which frames of the low-delay TIDs are combined (aggregated) to the TB PPDU. At this time, the multi-TID A-MPDU included in the TB PPDU can include (aggregate) frames of the low-delay TIDs regardless of the Preferred AC subfield value indicated by the Trigger frame. That is, an STA responding to a TB PPDU in an R-TWT SP can respond to a multi-TID A-MPDU including a low-latency TID as a TB PPDU regardless of the Preferred AC information indicated through the Trigger frame.

[0266] However, an STA responding to a TB PPDU may respond by including a frame of a TID other than the low-latency TID in the TB PPDU if the frame of the low-latency TID no longer exists. In this case, an STA responding by including a frame of a TID other than the low-latency TID in the TB PPDU must transmit a multi-TID A-MPDU in the TB PPDU according to the rules below.

[0267] - Prioritize including MPDUs corresponding to the low-latency TID of the R-TWT SP.

[0268] - After that, MPDUs corresponding to Preferred AC are included first.

[0269] - After that, MPDUs of ACs with higher priority than Preferred AC are included first.

[0270] - Including the remaining MPDUs

[0271] Additionally, it is possible to first include MPDUs corresponding to low-latency TIDs, and then include MPDUs of other TIDs of the AC corresponding to the low-latency TID in the TB PPDU. For example, if only one of two TIDs corresponding to a specific AC is designated as a low-latency TID, the MPDU corresponding to the low-latency TID may be first included in the A-MPDU, and then the MPDU corresponding to the remaining TID may be included. In this case, the MPDUs of other ACs (of TIDs) that do not correspond to the low-latency TID are included after the MPDUs corresponding to the remaining TID.

[0272] <R-TWT SP에서의 채널 액세스 관리 방법>

[0273] As considered in the embodiments of the present invention, when establishing an R-TWT SP, information about a TID to be considered as a low-delay TID can be indicated through a broadcast TWT parameter set field, and only MPDUs of the low-delay TID can be transmitted within the R-TWT SP.

[0274] Conventional Wi-Fi allows Scheduled STAs in a broadcast TWT SP to initiate transmissions by performing their own channel access (rather than channel access via trigger frames) within the broadcast TWT SP via EDCA or similar. Considering this, even in an R-TWT SP, which can be considered a type of broadcast TWT, Scheduled STAs may be permitted to perform their own channel access via EDCA or similar.

[0275] In this case, the R-TWT SP, which restricts MPDU transmission of TIDs other than the low-latency TID, can be understood as a TID-restricted channel access section, which has not been considered in conventional Wi-Fi. Therefore, Scheduled STAs performing channel access within the R-TWT SP perform channel access that takes TID restrictions into account.

[0276] According to one embodiment of the present invention, Scheduled STAs performing channel access within an R-TWT SP may perform a conventional EDCA operation, but may attempt to acquire a TXOP only through an EDCAF corresponding to a low-latency TID for an UL direction. More specifically, when a Scheduled STA of an R-TWT SP attempts to acquire a TXOP by performing its own channel access, it may need to perform contention for channel access only through the EDCAF of an AC corresponding to the low-latency TID. For example, when a specific R-TWT SP is established, the low-latency TID of the R-TWT SP may be indicated as TID 4 to TID 7, and the TID 4 to TID 7 may be TIDs corresponding to AC_VI and AC_VO. In this case, if a Scheduled STA of the specific R-TWT SP attempts to perform channel access via EDCA within the R-TWT SP, the Scheduled STA may need to acquire a TXOP only through the EDCAFs of AC_VI and AC_VO.

[0277] Meanwhile, in the R-TWT SP, the EDCAF of another AC that does not correspond to the AC indicated by the low-latency TID may not participate in contending for TXOP acquisition within the R-TWT SP. That is, the other EDCAF may be understood to be inactive. The operation performed when a specific EDCAF does not participate in contending for TXOP acquisition (i.e., is inactive) may utilize at least one of the operations below. In this case, the operation of not participating in contending for TXOP acquisition of the EDCAF described below may be performed in the TID-R-TWT SP to which a transmission restriction for the TID is applied. In this case, the TID-R-TWT SP may be verified through at least one of whether the value of the DL / UL TID Bitmap Valid subfield is 1 and whether the value of the broadcast TWT Recommendation field is a specific value.

[0278] 1) First, the channel access procedure by EDCA of an AC that does not correspond to an AC of a TID allowed to be transmitted within an R-TWT SP may not decrease the back-off counter because the channel status by carrier sensing (CS) of the channel is always determined to be occupied within the R-TWT SP.

[0279] That is, an EDCAF that does not participate in contending for TXOP acquisition within the R-TWT SP can consider the Medium within the R-TWT SP as being virtually busy. That is, an EDCAF that does not participate in contending may not decrease the backoff counter during the R-TWT SP. At this time, an EDCAF that does not participate in contending for TXOP acquisition within the R-TWT SP may suspend the backoff operation without evaluating the Medium state within the R-TWT SP.

[0280] 2) Second, in the channel access procedure by EDCA of an AC that does not correspond to an AC of a TID allowed to be transmitted within an R-TWT SP, the back-off counter may remain at a value of 0 even if it reaches 0.

[0281] That is, an EDCAF that does not participate in contending for TXOP acquisition within an R-TWT SP can consider the transmission queue of the corresponding AC within the R-TWT SP to be empty. In other words, an EDCAF that does not participate in contending can keep the backoff counter at 0 without attempting transmission even if the backoff counter reaches 0 during an R-TWT SP.

[0282] 3) Thirdly, in the channel access procedure by EDCA of an AC that does not correspond to an AC of a TID allowed to be transmitted within an R-TWT SP, if the backoff counter reaches 0, a new backoff counter can be selected again to restart the backoff procedure.

[0283] That is, an EDCAF that does not participate in contending for TXOP acquisition within an R-TWT SP may need to invoke a new backoff procedure when the backoff counter reaches 0 within the R-TWT SP. That is, an EDCAF that does not participate in contending may initiate a new backoff procedure without attempting to transmit once the backoff procedure is completed during an R-TWT SP.

[0284] At this time, the operations 1), 2), and 3) described above are operations performed by EDCAFs corresponding to each AC, but in the present invention, for the convenience of explanation, it can be described that the entity performing channel access and Backoff procedure, etc. is an STA (e.g., Scheduled STA). That is, it can be expressed that the STA does not transmit an MPDU corresponding to a specific TID, and this can mean that among the EDCAFs of the EDCA operation performed by the STA, the EDCAF of the AC corresponding to the specific TID does not participate in contending for TXOP acquisition. At this time, the TXOP can mean both a Transmission opportunity that can operate a frame exchange sequence more than once and a channel access opportunity that can perform a single frame transmission (and response frame reception).

[0285] Meanwhile, since each AC of EDCA corresponds to two TIDs, only one of the two TIDs corresponding to a specific AC may be a low-latency TID, and the other TID may not be a low-latency TID. In this case, the specific AC may be considered to be the AC corresponding to the low-latency TID. That is, even though a specific TID is not considered a low-latency TID within the R-TWT SP (it is not indicated as a low-latency TID by the Scheduling AP), the EDCAF of the corresponding AC may still participate in contending for TXOP acquisition.

[0286] Alternatively, if only one of the two TIDs corresponding to a specific AC is a low-latency TID and the other TID is not a low-latency TID, the specific AC may be considered not to be an AC corresponding to the low-latency TID. In this case, the EDCAF corresponding to the specific AC does not participate in contending for TXOP acquisition, and the MPDU for the low-latency TID among the two TIDs corresponding to the specific AC may be transmitted in the transmission performed through the TXOP acquired by the other EDCAF. In this case, the method in which the EDCAF corresponding to the specific AC does not participate in contending for TXOP acquisition may be the same as / similar to the method in which the EDCAF of the AC that does not correspond to the low-latency TID described above does not perform channel access.

[0287] If the Scheduled STA of the R-TWT SP participates in the contending for TXOP acquisition only with the EDCAF corresponding to a specific TID (e.g., low-latency TID) by method 1) and does not participate in the contending for TXOP acquisition through other EDCAFs, the other EDCAFs may perform an operation to stop backoff regardless of the medium status (IDLE or BUSY) confirmed through the PHY CS. This may be similar to an operation in which the medium is considered busy only for some of the EDCAFs of the Scheduled STA. Accordingly, the Scheduled STA may perform the operation 1) described above by setting the Network Allocation Vector (NAV) to a non-zero value during the R-TWT SP for the EDCAF that does not correspond to the low-latency TID. In this case, the NAV may be a per-EDCAF NAV applied to each EDCAF, unlike the NAV used in conventional Wi-Fi. At this time, the per-EDCAF NAV may be a kind of timer applied to each EDCAF, and the EDCAF with a non-zero per-EDCAF NAV may have to behave in a manner of not decreasing the backoff counter, similar to when the medium is virtually busy. At this time, the per-EDCAF NAV may be maintained as a non-zero value only within the R-TWT SP. That is, the per-EDCAF NAV is set to a value considering the duration of the R-TWT SP at the start of the R-TWT SP, and the value of the per-EDCAF may be continuously decreased during the R-TWT SP. However, if the R-TWT SP ends earlier than the scheduled duration, the per-EDCAF NAV may be initialized (reset, i.e. set to 0) together with the termination of the R-TWT SP.Conversely, if the R-TWT SP is extended beyond the scheduled duration, the per-EDCAF NAV may also be reset to take into account the extended period of the R-TWT SP. Alternatively, the R-TWT Scheduled STA may set the per-EDCAF NAVs of the EDCAFs that do not correspond to the low-latency TID to non-zero values ​​when the R-TWT SP starts, and initialize all per-EDCAFs to 0 when the R-TWT SP ends. Alternatively, the R-TWT SP-NAV, which is commonly applied to the EDCAFs that do not correspond to the low-latency TID, may be utilized instead of the per-EDCAF NAV. When the R-TWT SP-NAV has a non-zero value, the remaining EDCAFs, except for the EDCAFs corresponding to the TIDs considered as the low-latency TIDs in the R-TWT SP, may not participate in contending for TXOP acquisition.

[0288] What is meant by being commonly applied to EDCAFs that do not correspond to the low-latency TID above is that it is commonly applied to all EDCAFs (AC_VO, AC_VI, AC_BE, AC_BK), but may mean that it is ignored by EDCAFs corresponding to the low-latency TID. That is, the timer (R-TWT SP-NAV) that is maintained with a non-zero value during the R-TWT SP is a timer that is commonly applied to all EDCAFs, and may be a timer that is ignored by EDCAFs corresponding to the low-latency TID. That is, the EDCAF corresponding to the low-latency TID may decrease the Backoff counter or initiate transmission for acquiring a TXOP even in the section where the timer is not 0.

[0289] Since the above R-TWT SP-NAV can be managed in the same / similar manner as the above-described per-EDCAF NAV, a detailed description thereof is omitted.

[0290] 1) In order to perform the operation, the Scheduled STA may set the per-EDCAF NAV of specific EDCAFs by considering the duration of the specific R-TWT SP when the specific R-TWT SP starts. At this time, the per-EDCAF NAV may be used in the Virtual CS (carrier sense) mechanism together with the conventional NAV commonly used by EDCAFs. That is, even if the per-EDCAF NAV is 0, each EDCAF may have to determine the result of the Virtual CS as busy if the NAV is a non-zero value. On the other hand, even if the NAV is 0, if the per-EDCAF NAV of a specific EDCAF is a non-zero value, the specific EDCAF may not have to decrease the Backoff counter as if the result of the Virtual CS is busy.

[0291]

[0292] If a Scheduled STA of an R-TWT SP participates in contending for TXOP acquisition only with an EDCAF corresponding to a specific TID (e.g., a low-latency TID) by the method b) above, other EDCAFs may have to call the backoff procedure again when the R-TWT SP ends. More specifically, EDCAFs whose backoff counters were maintained as 0 during the R-TWT SP through the operation 2) described above may have to call a new backoff procedure when the R-TWT SP ends. In this case, the operation of calling the backoff procedure again may mean regenerating the backoff counter.

[0293] The reason why EDCAFs must call the backoff procedure at the end of the R-TWT SP is as follows.

[0294] 2) If some EDCAFs do not participate in contending for TXOP acquisition through method 2), some of the EDCAFs may maintain the backoff counter value as 0 when the R-TWT SP ends. This may be because some of the EDCAFs consider the transmission queue of the AC associated with them to be empty, and thus do not attempt transmission or regenerate the backoff counter even though the backoff counter is 0. In this case, when the R-TWT SP ends, some of the EDCAFs (whose backoff counter was maintained as 0) may immediately attempt transmission similar to the case where a frame to be transmitted is generated in the AC's transmission queue. In other words, two or more EDCAFs may attempt transmission at the same time when the R-TWT SP ends, and the same may apply to the EDCAFs of other STAs. Since multiple EDCAFs can attempt to transmit (acquire TXOP) simultaneously at the end of the R-TWT SP, there is a high probability of collision. In order to prevent collision, the EDCAF whose backoff counter was maintained at 0 through the operation of 2) described above may need to create a new backoff counter (call the backoff procedure) at the end of the R-TWT SP. In this case, each EDCAF that calls the new backoff procedure at the end of the R-TWT SP calls the new backoff procedure while maintaining the CW[AC] (Contention Window) and QSRC[AC] (QoS STA Retry Counter) of the corresponding AC at the existing values.

[0295]

[0296] If a Scheduled STA of an R-TWT SP participates in contending for TXOP acquisition only with an EDCAF corresponding to a specific TID (e.g., a low-latency TID) by the method 3) above, other EDCAFs may have to invoke a new backoff procedure when the backoff procedure is completed during the R-TWT SP. In other words, EDCAFs that do not correspond to a low-latency TID may have to invoke a new backoff procedure without initiating transmission for TXOP acquisition when the backoff counter becomes 0 (at the current slot boundary or the next slot boundary). This can be understood as an operation of repeating the backoff procedure of an EDCAF corresponding to a different TID in order to avoid transmitting MPDUs of other TIDs that are not considered low-latency TIDs for the specific R-TWT SP. In this case, an EDCAF invoking a new backoff procedure may have to invoke the new backoff procedure without changing the existing CW[AC] and QSRC[AC] of the corresponding AC.

[0297] Meanwhile, the method of not transmitting an EDCAF that does not correspond to a low-delay TID during an R-TWT SP through the operations 1), 2), and 3) described above may be applied only when a queuing frame (MSDU, A-MSDU, MMPDU, etc.) exists in the transmit (hereinafter referred to as TX) queue of the EDCAF that corresponds to the low-delay TID. That is, even in the R-TWT SP, if the TX queue of the EDCAF that corresponds to the low-delay TID is empty, the inactive state of the EDCAF that does not correspond to the low-delay TID may be released (i.e., become active). In this case, if only traffic corresponding to a TID other than the low-delay TID exists in the TX queue of the EDCAF that corresponds to the low-delay TID, it is also possible that the TX queue of the EDCAF that corresponds to the low-delay TID may be considered to be empty. That is, the empty TX queue of the EDCAF corresponding to the low-latency TID can mean either 1. no frame exists in the TX queue, or 2. no frame corresponding to the low-latency TID exists in the TX queue.

[0298] Alternatively, the method of not transmitting EDCAFs that do not correspond to low-latency TIDs during the R-TWT SP through operations 1), 2), and 3) may be applied until a separate instruction is received from the AP. More specifically, the AP may perform signaling to release the restriction on TXOP acquisition attempts related to low-latency TIDs during the R-TWT SP. The signaling may be signaling that the AP instructs when it determines that member STAs of the R-TWT SP no longer have traffic corresponding to low-latency TIDs. That is, the AP performs signaling to release the restriction on TXOP acquisition attempts related to low-latency TIDs when it determines that member STAs of the R-TWT SP no longer have traffic corresponding to low-latency TIDs during the R-TWT SP, and a non-AP STA that is a member of the R-TWT SP may change the EDCAF that does not correspond to low-latency TIDs to an active state (a state in which TXOP acquisition attempts are possible) upon receiving the signaling. In the embodiments described below, the condition for releasing the channel access restriction applied to the EDCAF that does not correspond to the low-delay TID is mainly considered to be the case where the transmit queue of the EDCAF corresponding to the low-delay TID is changed to empty, but it is possible to change the condition and apply it to the case where the AP performs signaling to release the TXOP acquisition attempt restriction related to the low-delay TID. That is, in the embodiments described below, the operation performed based on whether the transmit queue of the EDCAF corresponding to the low-delay TID is empty can be appropriately understood as being replaced with an operation performed based on whether a signaling to release the TXOP acquisition attempt restriction related to the low-delay TID is received from the AP.

[0299] To elaborate on 1) mentioned above, the timer applied to the EDCAF that does not correspond to the low-delay TID may be applied only when there is a queuing frame in the TX queue of the EDCAF that corresponds to the low-delay TID. In other words, if the TX queue of the EDCAF that corresponds to the low-delay TID is empty, the EDCAF that does not correspond to the low-delay TID may also be allowed to decrease the backoff counter or initiate transmission to acquire a TXOP.

[0300] To explain 2) in more detail, the operation of considering the Tx queue of the EDCAF that does not correspond to the low-delay TID as empty may be applied only when a queueing frame exists in the TX queue of the EDCAF that corresponds to the low-delay TID. In other words, if the TX queue of the EDCAF that corresponds to the low-delay TID is empty, the TX queue of the EDCAF that does not correspond to the low-delay TID may not be considered empty.

[0301] To explain 3) in more detail, the operation of re-invoking the backoff procedure of the EDCAF that does not correspond to the low-delay TID may be applied only when there is a queueing frame in the TX queue of the EDCAF that corresponds to the low-delay TID. That is, if the TX queue of the EDCAF that corresponds to the low-delay TID is empty, the EDCAF that does not correspond to the low-delay TID can initiate transmission for acquiring a TXOP without invoking a new backoff procedure when the backoff counter becomes 0.

[0302] In addition, the operations of 1), 2), and 3) described above may be applied to all EDCAFs of STAs that are not members of the R-TWT SP. That is, STAs that are not members of the R-TWT SP may not attempt channel access during the R-TWT SP by managing the channel access procedures of all EDCAFs in the same manner as the management method of EDCAFs that do not correspond to the low-latency TID considered in 1), 2), and 3) described above.

[0303] To describe the operation of an STA that is not a member of an R-TWT SP in more detail with respect to a), an STA that is not a member of an R-TWT SP can manage the backoff procedure of each EDCAF using a timer that is commonly applied to all EDCAFs. At this time, the timer is maintained as a non-zero value during the R-TWT SP, and during the non-zero period of the timer, each EDCAF considers the channel state to be the same as being busy and freezes the backoff procedure. In this way, an STA that is not a member of an R-TWT SP may not attempt channel access (TXOP acquisition) during the R-TWT SP.

[0304] To explain the behavior of an STA that is not a member of an R-TWT SP in more detail with respect to 2), an STA that is not a member of an R-TWT SP may consider the TX queues of all EDCAFs as empty. In this case, the time period during which the STA that is not a member of an R-TWT SP considers the TX queues as empty may be during an R-TWT SP of which it is not a member. In this case, an STA that is not a member of an R-TWT SP may invoke a new backoff procedure for each EDCAF whose backoff counter is 0 when an R-TWT SP of which it is not a member is terminated. In this way, an STA that is not a member of an R-TWT SP may not attempt channel access (TXOP acquisition) during an R-TWT SP.

[0305] To explain the operation of an STA that is not a member of the R-TWT SP in more detail with respect to 3), an STA that is not a member of the R-TWT SP can call a new backoff procedure when the backoff procedure of each EDCAF is completed. At this time, the condition for the STA that is not a member of the R-TWT SP to newly call the backoff procedure of each EDCAF may be that the time point at which the backoff procedure of each EDCAF is completed corresponds to a time point corresponding to an R-TWT SP of which it is not a member. In this way, an STA that is not a member of the R-TWT SP may not attempt channel access (TXOP acquisition) during the R-TWT SP.

[0306]

[0307] That is, all EDCAFs of STAs that are not members of the R-TWT SP can be made inactive (not attempting to acquire TXOP) during the R-TWT SP through methods such as 1), 2), and 3) described above. This can be understood as equivalent to STAs that are not members of the R-TWT SP considering all EDCAFs as EDCAFs that do not correspond to low-latency TIDs, regardless of the type of TID indicated / promised as a low-latency TID in the R-TWT SP. In this case, the method by which STAs that are not members of the R-TWT SP manage each EDCAF is the same / similar to the method of managing EDCAFs that do not correspond to low-latency TIDs described above, so a detailed description thereof will be omitted.

[0308] FIG. 20 illustrates an example of an Enhanced Distributed Channel Access (EDCA) operation for channel access in a limited TWT SP according to one embodiment of the present invention.

[0309] Referring to FIG. 20, an R-TWT SP considering TID4 to TID7 as low-delay TIDs is started after a Beacon frame transmitted by the AP. The R-TWT SP is an R-TWT SP considering TID4 to TID7 as low-delay TIDs, and is an R-TWT SP in which transmission of MPDUs corresponding to TIDs other than low-delay TIDs is restricted. A non-AP STA, which is a Scheduled STA of the R-TWT SP, may stop contending for TXOP acquisition of an EDCAF other than the EDCAF corresponding to the low-delay TID in order not to transmit MPDUs other than low-delay TIDs within the R-TWT SP. That is, the Scheduled STA of the R-TWT SP attempts channel access only through the EDCAF of the AC corresponding to the low-delay TID within the R-TWT SP period. At this time, the operation illustrated in one embodiment of FIG. 20 is a contending non-participation method for TXOP acquisition using the method 1) described above.

[0310] As illustrated in FIG. 20, a non-AP STA can only perform an operation of decreasing the backoff counter of an EDCAF corresponding to a low-latency TID within an R-TWT SP. More precisely, among the EDCAFs of a non-AP STA, only the EDCAF corresponding to a low-latency TID can perform an operation of decreasing the backoff counter at a slot boundary. That is, among the EDCAFs of a non-AP STA, the EDCAFs of AC_BK and AC_BE corresponding to TID 0 to TID 3 may have to perform an operation (decision) to maintain the backoff counter without decreasing it at every slot boundary within the R-TWT SP, regardless of whether each slot is IDLE / BUSY.

[0311] A non-AP STA, which is a scheduled STA of an R-TWT SP, can stop contending for TXOP acquisition of an EDCAF other than the EDCAF corresponding to the low-delay TID in order to not transmit an MPDU other than the low-delay TID within the R-TWT SP. That is, a scheduled STA of an R-TWT SP attempts channel access only through the EDCAF of the AC corresponding to the low-delay TID within the R-TWT SP section. In this case, the operation illustrated in one embodiment of FIG. 20 is a method of non-participation in contending for TXOP acquisition using the method 1) described above.

[0312] A non-AP STA can only perform the operation of decreasing the backoff counter of the EDCAF corresponding to the low-latency TID within the R-TWT SP. More precisely, among the EDCAFs of the non-AP STA, only the EDCAF corresponding to the low-latency TID can perform the operation of decreasing the backoff counter at the slot boundary. That is, among the EDCAFs of the non-AP STA, the EDCAFs of AC_BK and AC_BE corresponding to TID 0 to TID 3 may perform the operation (decision) of maintaining the backoff counter without decreasing it at each slot boundary within the R-TWT SP, regardless of whether each slot is IDLE / BUSY.

[0313] Additionally, although not illustrated in FIG. 20, non-AP STAs that are not members of the R-TWT SP keep all EDCAFs inactive during the R-TWT SP. That is, non-AP STAs that are not members of the R-TWT SP do not attempt to acquire a TXOP by not decreasing the Backoff counter of each EDCAF during the R-TWT SP, considering the transmit queues of all EDCAFs as empty, or calling a new Backoff procedure when the Backoff procedure of each EDCAF is completed.

[0314]

[0315] FIG. 21 illustrates an example of a method for transmitting traffic for TIDs allowed for transmission and TIDs restricted from transmission in a restricted TWT SP according to one embodiment of the present invention.

[0316] Referring to Fig. 21, after the Beacon frame transmitted by the AP, an R-TWT SP that considers TID4 to TID7 as low-delay TIDs is initiated. That is, within the R-TWT SP, AC_VI and AC_VO are EDCAFs corresponding to low-delay TIDs, and AC_BE and AC_BK are EDCAFs that do not correspond to low-delay TIDs. Accordingly, among the EDCAFs of non-AP STAs, which are Scheduled STAs of the R-TWT SP, AC_VO and AC_VI, which are EDCAFs corresponding to low-delay TIDs, are active, and AC_BE and AC_BK are inactive.

[0317] Non-AP STA, which is a Scheduled STA of R-TWT SP, obtains TXOP through AC_VO, which is a low-latency EDCAF, and transmits frames of TID6 and TID7 corresponding to AC_VO and frames of TID4 and TID5 corresponding to AC_VI through PPDU#1.

[0318] After the Non-AP STA transmits PPDU#1, there are no more queueing frames in the transmit queues of AC_VI and AC_VO.

[0319] In this case, since the transmit queues of all EDCAFs corresponding to the TIDs indicated / promised as low-delay TIDs in the R-TWT SP become empty, the remaining EDCAFs that do not correspond to the low-delay TIDs, i.e., AC_BK and AC_BE, are switched to the active state.

[0320] The non-AP STA acquires TXOP through AC_BE (i.e., AC_BE becomes the TXOP holder) and transmits a frame (MSDU, A-MSDU, etc.) corresponding to TID0 or TID3 through PPDU#2.

[0321] Additionally, although not illustrated in FIG. 21, non-AP STAs that are not members of the R-TWT SP keep all EDCAFs inactive during the R-TWT SP. That is, non-AP STAs that are not members of the R-TWT SP do not attempt to acquire a TXOP by not decreasing the Backoff counter of each EDCAF during the R-TWT SP, considering the transmit queues of all EDCAFs as empty, or calling a new Backoff procedure when the Backoff procedure of each EDCAF is completed.

[0322] <TID-to-Link mapping을 고려한 채널 액세스 관리 방법>

[0323] TID-to-Link mapping refers to a mechanism that allows two MLDs that have established a multi-link setup to determine which TID to transmit / receive through which Link. TID-to-Link mapping can be determined for the DL and UL directions respectively, and when TID-to-Link mapping negotiation is performed between an AP MLD and a STA MLD, the AP MLD and the STA MLD may need to determine a transmission Link by considering the TID of the frame they transmit. For example, an AP MLD and a (non-AP) STA MLD may have performed a multi-link setup through two Links, and may have negotiated to map TID 0 to TID 3 to Link 1 and TID 4 to TID 7 to Link 2 for the DL direction. In this case, when the AP MLD transmits DL traffic to the STA MLD, traffic (MSDU, MPDU, etc.) corresponding to TID 0 to TID 3 must be transmitted only through Link 1, and traffic corresponding to TID 4 to TID 8 must be transmitted only through Link 2.

[0324] Similarly, a non-AP STA MLD may also need to transmit UL traffic considering TID-to-Link mapping negotiation in the UL direction. For example, an AP MLD and a (non-AP) STA MLD may have performed a multi-link setup over two Links and negotiated to map TID 0 to TID 3 to Link 1 and TID 4 to TID 7 to Link 2 for the UL direction. In this case, when the non-AP STA MLD transmits UL traffic to the AP MLD, the traffic (MSDU, MPDU, etc.) corresponding to TID 0 to TID 3 must be transmitted only over Link 1, and the traffic corresponding to TID 4 to TID 8 must be transmitted only over Link 2.

[0325] In this way, if two MLDs that performed multi-link setup performed TID-to-Link mapping negotiation (a mapping other than the default TID-to-link mapping mode), the two MLDs may have to transmit traffic for a specific TID only to a specific Link, taking the TID-to-Link mapping into account. In other words, they may not attempt to transmit traffic for a specific TID on a Link where the specific TID is not mapped in the transmission direction.

[0326] Accordingly, when a non-AP STA MLD transmits traffic of a specific TID to an AP MLD, it may not attempt to transmit traffic corresponding to the specific TID on a link to which the specific TID is not mapped. In this case, the non-AP STA MLD may not perform channel access through the EDCAF corresponding to the specific TID in a non-AP STA operating on a link to which the specific TID is not mapped in the UL direction. In other words, the non-AP MLD may not perform (participate in) contending for TXOP acquisition through some of the EDCAFs of STAs operating on the specific Link when the specific TID is not mapped in the UL direction on the specific Link.

[0327] If a specific Link of a non-AP STA MLD is disabled (no TID is mapped), an STA of a non-AP STA MLD operating on the specific Link may not perform channel access through any EDCAF. In other words, an STA of a non-AP STA MLD operating on a Disabled Link (no TID is mapped) may be understood as having all EDCAFs disabled. At this time, an EDCAF disabled according to the TID-to-Link mapping status may have a state similar to an EDCAF disabled within an R-TWT SP (see FIG. 20). That is, an EDCAF disabled according to the TID-to-Link mapping status may not participate in contending for TXOP acquisition by utilizing the operations 1), 2), and 3) described above. However, depending on the TID-to-Link mapping status, the deactivated EDCAF may not perform an operation that takes into account the duration of the R-TWT SP and may remain in the deactivated state until the TID-to-Link mapping is changed.

[0328] Another difference is that, with respect to the R-TWT SP, a disabled EDCAF is activated when the R-TWT SP is terminated, whereas depending on the TID-to-Link mapping status, a disabled EDCAF can be activated when the TID-to-Link mapping is changed to default mode, or when a TID-to-Link mapping negotiation is performed where the TID corresponding to the disabled EDCAF is mapped to the Link (for the UL direction).

[0329]

[0330] <R-TWT SP의 단계적인 운용 방법>

[0331] According to one embodiment of the present invention described above, the AP can set two types of R-TWT SPs. One of the two types of R-TWT SPs can be a SP with stricter rules that only allow transmission of low-latency TIDs, and the other can be a flexible SP that also allows transmission of other TIDs when low-latency TIDs are not present.

[0332] In the present invention, two types of R-TWT SPs are considered to allow for a choice between a priority enhancement method for low-latency TIDs and more efficient utilization of the time interval corresponding to the R-TWT SP. The characteristics of the two types of R-TWT SPs are as follows.

[0333] 1) If only low-latency TID traffic can be transmitted within the R-TWT SP, only some time intervals within the R-TWT SP may be utilized for low-latency TID services, and the remaining time intervals may be wasted.

[0334] 2) If traffic transmission of other TIDs is allowed within the R-TWT SP, transmission of other STAs with low-latency TIDs may be delayed while traffic of other TIDs is being serviced.

[0335] Therefore, AP and non-AP may want to operate R-TWT SP in different ways depending on their purpose, and may selectively operate / participate as a member one of the two R-TWT SPs as considered in the present invention.

[0336] However, if the decision on whether traffic of a TID other than a low-latency TID can be transmitted is made on a per-R-TWT SP basis, a specific R-TWT SP may experience a continuously wasted time interval, and other R-TWT SPs may experience a problem in which processing of low-latency TID traffic is delayed.

[0337] To solve this problem, according to one embodiment of the present invention, it is possible to divide the intervals of a single R-TWT SP and operate them with different policies. More specifically, in some time intervals of a single R-TWT SP, only traffic of a low-latency TID may be allowed to be transmitted, and in the remaining intervals, traffic of a TID other than the low-latency TID may be allowed to be transmitted. However, since the remaining intervals are also time intervals within the R-TWT SP, transmission of traffic of the low-latency TID is still performed with priority, and transmission of traffic of other TIDs is allowed only when there is no traffic of the low-latency TID.

[0338] At this time, the time interval to which different operation policies are applied can be determined by a portion and the remaining portion of the Duration of the R-TWT SP. For example, the R-TWT SP corresponding to the first half of the Duration of the R-TWT SP can be a period in which only low-latency TID transmission is allowed, and the R-TWT SP corresponding to the remaining half can be a period in which other TID transmission is allowed. At this time, information related to the time interval to which different policies are applied during the Duration of the R-TWT SP can be information that the AP indicates together in the TWT element when indicating the R-TWT SP. At this time, if the AP does not indicate information related to the time interval to which different policies are applied during the Duration of the R-TWT SP, the pre-arranged time interval (ratio) of the R-TWT SP can be determined to be a time interval in which only low-latency TID transmission is allowed. In other words, the time interval of the R-TWT SP corresponding to the pre-arranged ratio between the AP and the non-AP STA can be determined as a time interval in which only low-latency TIDs can be transmitted. At this time, the remaining time interval may be a time interval in which traffic of a TID other than the low-latency TID can be transmitted when a low-latency TID does not exist. In this case, the non-AP STA must transmit only traffic corresponding to the low-latency TID during the time interval in which only the low-latency TID can be transmitted among the R-TWT SPs, and may transmit traffic of a TID other than the low-latency TID during the remaining time interval.

[0339] Alternatively, the rule for changing the operating policy (method) within the R-TWT SP (from a method of transmitting only frames of the low-latency TID to a method of restrictively allowing transmission of frames of other TIDs than the low-latency TID) may be determined by whether a certain amount of time has elapsed since the start of the R-TWT SP. More specifically, it is possible that before a predetermined amount of time has elapsed since the start of the R-TWT SP, only transmission of frames of the low-latency TID is allowed, and after the predetermined amount of time has elapsed, transmission of frames of other TIDs than the low-latency TID is allowed. For example, the time period corresponding to the first 1 TU in the R-TWT SP may be a period in which transmission of only frames of the low-latency TID is allowed, and the remaining time periods may be periods in which transmission of frames of other TIDs than the low-latency TID is allowed.

[0340] In another way, the rule for changing the operation policy (method) within the R-TWT SP may be determined based on whether the R-TWT SP overlaps with a specific other time interval. More specifically, the time interval of the R-TWT SP that overlaps with the quiet interval (duration) set for the protection purpose of the R-TWT SP may be an interval in which only frames of a low-delay TID are allowed to be transmitted. In this case, the remaining R-TWT SP intervals that do not overlap with the quiet interval may be a time interval in which transmission of frames of a TID other than the low-delay TID is allowed. In this case, the time interval set together to specify the interval in which the operation method of the R-TWT SP is changed may be a time interval other than the quiet interval. In this case, the other time interval may be a time interval set to start at the same time as the start time of the R-TWT SP. In this case, the other time interval may be set by the AP to specify the time point in which the operation method of the R-TWT SP is changed.

[0341]

[0342] Alternatively, the method of changing the operation method within the R-TWT SP may be that the AP performs an explicit instruction. More specifically, the AP may perform signaling for the purpose of changing the operation method during the R-TWT SP period. At this time, the signaling may be performed through a specific frame that has been agreed upon, or through the A-Control (indicated through the HT Control field of the MAC header) or the More Data subfield (a bit included in the Frame Control field of the MAC header). At this time, the signaling may be performed through a frame (group addressed, broadcast) rather than an individually addressed frame.

[0343] For example, an AP may transmit a pre-arranged frame (e.g., a CF-END frame) to allow transmission of frames of a TID other than the low-latency TID within the R-TWT SP interval. A non-AP STA that receives a pre-arranged frame from the AP during an R-TWT SP interval in which only low-latency TID frames can be transmitted may recognize that the operation method for the remaining R-TWT SP interval has changed to allow transmission of frames of a TID other than the low-latency TID.

[0344] As another example, an AP may set the More Data subfield of a non-individually addressed frame (group addressed frame) to 0 to allow transmission of frames with TIDs other than the low-latency TID within the R-TWT SP interval. That is, the More Data subfield transmitted by the AP within the R-TWT SP interval may be utilized to indicate a change in the operation method of the R-TWT SP, rather than to indicate whether the AP has group addressed bufferable units (BUs). A non-AP STA that determines that the More Data subfield of a group addressed frame received from the AP is set to a specific value (e.g., 0) during an R-TWT SP interval in which only low-latency TID frames can be transmitted may recognize that the operation method for the remaining R-TWT SP interval has changed to allow transmission of frames with TIDs other than the low-latency TID. At this time, a way to distinguish whether a frame received from the AP is a group addressed frame may be to check whether the RA (receiver addressed) of the MAC header of the received frame includes a group address. In this way, if the More Data subfield is used to indicate the operation method of the R-TWT SP, while the R-TWT SP that allows transmission of frames of TIDs other than the low-delay TID is in progress, the R-TWT SP may be changed to an R-TWT SP that only allows transmission of frames of the low-delay TID if the value indicated in the More Data subfield is changed.That is, if the More Data subfield value of the group addressed frame transmitted by the AP is a specific value, only frame transmission of the low-latency TID is allowed in the R-TWT SP, and if the More Data subfield value is a different value, frame transmission of a TID other than the low-latency TID may be allowed in the R-TWT SP.

[0345]

[0346] FIG. 22 illustrates an example of how different operating policies are applied to different sections in a single limited TWT SP according to one embodiment of the present invention.

[0347] Referring to Fig. 22, an R-TWT SP that considers TID4 to TID7 as low-latency TIDs starts after the Beacon frame transmitted by the AP.

[0348] Among the time intervals corresponding to the R-TWT SP, the preceding time interval (Low latency TID only interval in Fig. 23) is an interval in which only transmission of low latency TID is allowed, and the remaining time interval (Low latency TID first interval in Fig. 22) is an interval in which transmission of traffic of other TIDs is allowed when traffic corresponding to the low latency TID no longer exists.

[0349] Therefore, when a non-AP STA that is a member of an R-TWT SP transmits Multi-TID A-MPDU#1 during a preceding time period among the time periods of the R-TWT SP, it transmits only the MPDUs of TID4 to TID7, which are low-delay TIDs of the R-TWT SP.

[0350] Non-AP STA transmits Multi-TID A-MPDU#2 after the previous time interval ends, aggregates TID0 to TID3 MPDUs together because frames of TID4 to TID7 no longer exist.

[0351]

[0352] FIG. 23 is a flowchart illustrating an example of the operation of a terminal according to an embodiment of the present invention.

[0353] Referring to FIG. 23, when a section in which only specific frames can be transmitted is set by an AP STA, a non-AP STA receives information related to a TID for traffic that can be transmitted in the set section from the AP STA, and can transmit traffic corresponding to the TID in the set section based on the received information.

[0354] Specifically, a non-AP STA receives a trigger frame that triggers transmission of a PPDU from an AP-STA (S23010). At this time, the trigger frame includes information indicating at least one TID (Traffic Identifier) ​​whose transmission is permitted in a TWT period, and the TWT period may mean a period in which transmission of traffic for the at least one TID having a specific transmission condition is permitted and transmission of traffic not having the specific transmission condition is restricted.

[0355] Specifically, as described in FIGS. 15 to 22, the R-TWT SP can be set so that transmission of traffic satisfying a specific condition is permitted by the AP, and transmission of traffic not satisfying the specific condition is restricted. In this case, whether or not the specific condition is satisfied is determined by transmitting information related to the TID corresponding to the traffic by the AP (e.g., information indicating the TID corresponding to the traffic satisfying the specific condition), and a non-AP STA can transmit and receive traffic corresponding to the TID transmitted from the AP within the TWT SP. At this time, the specific condition may be a condition related to transmission delay of the traffic (e.g., low-latency traffic, etc.), and transmission of traffic not having the specific condition may be restricted. Restricted transmission may mean that transmission is not possible during the R-TWT SP, transmission is possible under certain restrictions (e.g., transmission combined with MPDUs of traffic corresponding to TIDs that satisfy certain conditions, transmission combined with MPDUs of traffic corresponding to TIDs that satisfy certain conditions within a certain interval set within the TWT SP, etc.), or channel access through the EDCAF of ACs corresponding to TIDs that are not indicated by the AP is restricted.

[0356] Alternatively, the configured R-TWT SP may be reconfigured into multiple sections, and in at least one specific section, only traffic for a TID corresponding to traffic with a specific condition may be transmitted, and in sections other than at least one specific section, traffic for a TID corresponding to traffic that does not have the specific condition may be allowed to be transmitted under limited conditions (or specific restrictions). For example, if the R-TWT SP is configured with a first section and a second section, in the first section, only traffic for a TID corresponding to traffic with a specific condition (e.g., low latency, etc.) may be transmitted, and in the second section, traffic for a TID corresponding to traffic that does not have the specific condition may be allowed to be transmitted under limited conditions (or specific restrictions).

[0357] Information related to the TID may be transmitted in a bitmap format, where each bit may indicate a specific TID, and may be included in a trigger frame or a user information field containing information about each terminal in the trigger frame.

[0358] For example, if a Restricted TWT SP (hereinafter, R-TWT SP) that can only transmit low-latency traffic is set, each STA may be allowed to transmit only low-latency traffic within the R-TWT SP section, and may be restricted from transmitting traffic other than low-latency traffic. At this time, the types of traffic that STAs may transmit within a specific R-TWT SP may be restricted to traffic corresponding to TIDs indicated by the AP. That is, the AP may set TIDs of traffic that can be transmitted during the R-TWT SP during the process of setting up the R-TWT SP, and may notify the STAs of the set TIDs. In this case, non-AP STAs may only transmit traffic corresponding to the TIDs indicated by the AP within the R-TWT SP, and may be restricted from transmitting traffic corresponding to TIDs that are not indicated by the AP.

[0359] Thereafter, the non-AP STA can transmit a PPDU (Physical layer Protocol Data Unit) containing traffic corresponding to at least one TID to the AP within the TWT period (S23020).

[0360] At this time, the trigger frame can be transmitted within the TWT section.

[0361]

[0362] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will readily appreciate that the present invention can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single entity may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined manner.

[0363] The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims

1. In a wireless communication terminal of a wireless communication system, Transmitter and receiver; and Contains a processor, The above processor, Receive a trigger frame that triggers the transmission of PPDU from the AP (Access Point). The above trigger frame includes information indicating at least one TID (Traffic Identifier) ​​that is allowed to be transmitted during the TWT (Target Wake Time) period. The above TWT section represents a section in which transmission of traffic for at least one TID having a specific transmission condition is permitted and transmission of traffic not having the specific transmission condition is restricted. A wireless communication terminal that transmits a PPDU (Physical layer Protocol Data Unit) including traffic corresponding to at least one TID to the AP within the TWT period.

2. In paragraph 1, The above trigger frame is a wireless communication terminal transmitted within the above TWT section.

3. In paragraph 1, A wireless communication terminal, wherein an MPDU (Medium Access Control: MAC protocol data unit) including traffic corresponding to other TIDs except for at least one TID is combined with an MPDU of the PPDU including the traffic corresponding to the at least one TID and transmitted in the form of an A (Aggregated)-MPDU.

4. In paragraph 1, A wireless communication terminal that allows transmission of traffic for a TID corresponding to an access category of at least one of the above TIDs within the TWT section.

5. In paragraph 1, The above TWT section includes the first section and the second section, The above first section is a section in which only transmission of the traffic corresponding to at least one TID is permitted, A wireless communication terminal in which the second section is a section in which transmission of traffic corresponding to a TID other than at least one TID is permitted.

6. In paragraph 1, The above specific transmission conditions are conditions related to transmission delay of traffic in a wireless communication terminal.

7. In paragraph 1, A wireless communication terminal in which a channel access procedure by EDCA (Enhanced Distributed Channel Access) for ACs other than the AC corresponding to at least one TID is restricted within the above TWT section.

8. In paragraph 7, A wireless communication terminal in which the back off counter of the channel access procedure by the EDCA for the other AC within the TWT period is not decreased.

9. In paragraph 7, A wireless communication terminal in which the state of the channel for the channel access procedure by the EDCA for the other AC within the above TWT period is a busy state until the end of the TWT period.

10. In a traffic transmission method performed by a terminal in a wireless communication system, the method comprises: Receive a trigger frame that triggers the transmission of PPDU from the AP (Access Point). The above trigger frame includes information indicating at least one TID (Traffic Identifier) ​​that is allowed to be transmitted during the TWT (Target Wake Time) period. The above TWT section represents a section in which transmission of traffic for at least one TID having a specific transmission condition is permitted and transmission of traffic not having the specific transmission condition is restricted. A wireless communication method for transmitting a PPDU (Physical layer Protocol Data Unit) including traffic corresponding to at least one TID to the AP within the TWT period.

11. In Article 10, A wireless communication method in which the above trigger frame is transmitted within the above TWT section.

12. In paragraph 10, A wireless communication method in which an MPDU (Medium Access Control: MAC protocol data unit) including traffic corresponding to other TIDs excluding at least one TID is combined with an MPDU of the PPDU including the traffic corresponding to the at least one TID and transmitted in the form of an A (Aggregated)-MPDU.

13. In paragraph 10, A wireless communication method in which traffic for a TID corresponding to an access category of at least one TID is allowed to be transmitted within the TWT section.

14. In paragraph 10, The above TWT section includes the first section and the second section, The above first section is a section in which only transmission of the traffic corresponding to at least one TID is permitted, A wireless communication method in which the second section is a section in which transmission of traffic corresponding to a TID other than at least one TID is permitted.

15. In paragraph 10, A wireless communication method wherein the above specific transmission conditions are conditions related to transmission delay of traffic.

16. In paragraph 10, A wireless communication method in which a channel access procedure by EDCA (Enhanced Distributed Channel Access) for ACs other than ACs corresponding to at least one TID is restricted within the above TWT section.

17. In paragraph 16, A wireless communication method in which a back off counter of a channel access procedure by EDCA for a different AC within the TWT period is not decreased.

18. In paragraph 16, A wireless communication method in which the state of a channel for the channel access procedure by the EDCA for the other AC within the TWT period is a busy state until the TWT period ends.

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